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The last thing I did before I left the office on Tuesday night was write a short note to the editor of the following day's programme: "If you want a voice out of Homs tomorrow, my old mate Marie Colvin of the Sunday Times is there."

Hours later, she was dead, killed by a Syrian army attack on a building which was being used by anti-government activists as a base for visiting journalists who'd been smuggled in across the border. The award-winning young French photographer Remi Ochlik was also killed; three other Western journalists were injured.

This isn't going to be yet another tribute to one of the bravest and finest journalists of her generation (although Marie Colvin was both exceptionally brave and exceptionally talented). But I think it may be worth reflecting on why war correspondents put their lives in danger and whether the risks they run are worth it.

At a time when the reputation of journalists has probably never been lower (phone-hacking, police-bribing, celebrity-harassing -- you name it, journalists have, allegedly, done it), why not pause, just for a moment, to analyse a very different kind of journalism?

On Wednesday night's programme, the Syrian opposition activist Mahmoud Ali Hamad was adamant: the bravery of correspondents like Marie Colvin is saving lives. If it weren't for their presence, and their reporting, he said, government forces would be killing even more people, with even more impunity.

Marie herself reflected, in an address delivered just over a year ago, on the role of the war correspondent. "Someone has to go there and see what is happening. You can't get that information without going to places where people are being shot at, and others are shooting at you.

"The real difficulty is having enough faith in humanity to believe that enough people ... will care when your file reaches the printed page, the website or the TV screen. We do have that faith because we believe we do make a difference."

The key issue for Marie Colvin, according to of Channel 4 News, was to make sure that no one could ever say: "We didn't know." When people were being killed, when atrocities were being committed, it mattered to her that someone was there to bear witness and to tell the world.

The vast majority of journalists who are killed each year (46 last year, according to the ) are local reporters, killed in their home country. Their courage is even greater than that of the visiting correspondent, because they work in the knowledge that their homes and their families are constant potential targets -- and the truth they report is often a truth that their leaders, or other powerful interests, would much rather went unreported.

And as every foreign correspondent knows, the drivers, fixers, and translators who work with them often demonstrate the most stupendous courage. (Only once, in more than 40 years as a journalist, has a fixer walked out on me -- it was in Cambodia, during a military coup, when our fixer decided, quite rightly, that his family needed him more than we did.)

No journalist goes into a war zone believing it will be their last assignment. Risks are carefully assessed, precautions are taken, advice is sought. Only if the risks are deemed acceptable does the reporter head into danger. Every journalist who's been in Homs over the past three weeks, including the ´óÏó´«Ã½'s Paul Wood, with cameraman Fred Scott, has taken huge risks. Until this week, their calculation that those risks were within the bounds of what was acceptable seemed to have been borne out.

I have never forgotten the first words that were spoken to me on my first day in my first job: I'd been taken on as a trainee with Reuters news agency, and the then general manager, a big, bluff man called Gerald Long, welcomed us with the words: "I want you to understand one thing right away -- you're no use to me if you're dead."

Marie Colvin knew the dangers even better than most of her colleagues. She nearly lost her life in Sri Lanka in 2001, when she was caught in an army ambush and lost an eye. The man she had replaced as Middle East correspondent for the Sunday Times in the mid-80s, David Blundy, was killed just a few years later in El Salvador.

We should remember, though, that her death was just one of many this week in Homs. As I said on Wednesday's programme: "Most of those who died were people whose names we will never know: some of them civilians struck down by snipers as they ventured out to find food; others, fighters armed with light weapons taking on the full might of the Syrian army."

But the reason the death of a correspondent is worth marking is that it represents the silencing of a voice. And there are few voices as eloquent, or as powerful, as Marie Colvin's was.

Picture the scene: in one chair sits the leader of the richest and most powerful nation in the world. His name: Barack Obama, President of the United States of America.

In a second chair, sits the man who's probably about to take the title away from him. His name: Xi Jinping, Vice-President of the People's Republic of China.

Within the next year or so, Mr Xi is expected to have taken over as general secretary of the Chinese Communist Party and State President. During his decade in office, China is expected to overtake the US as the biggest economy in the world and will be well on the way to outspending it militarily as well. And this week, he's been in Washington on a getting-to-know-you visit.

We can get the jokes out of the way now. The current Chinese president is Hu Jintao, and has been the inevitable butt of innumerable jokes of the "President Who?" variety.

Mr Xi (pronounced She) will, I suspect, soon be subjected to countless "He said, Xi said" jokes. (The usually respectable magazine has already run a spoof headline competition: the winner was a headline for a story about a new Chinese high speed train line -- "Xi's got a ticket to ride.")

Silly jokes aside, President-to-be Xi could soon be one of the most important men on the planet. And the relationship he establishes with Mr Obama -- or with whoever is in the White House after the US presidential election in November -- will be a critical one.

At present, the relationship between the two countries is said by some analysts to be suffering from a "trust deficit". Washington doesn't trust what it sees as Beijing's military expansionism, or what it regards as unfair trade practices; Beijing distrusts the US's stated intention of building up a much more significant military presence in the Asia-Pacific region and its supposed penchant for expecting still to be treated as the only real global super-power.

Last November, on a visit to Australia, President said: "The United States is a Pacific power, and we are here to stay." Two months later, as he unveiled the new US defence strategy, he said: "We'll be strengthening our presence in the Asia-Pacific, and [military] budget reductions will not come at the expense of this critical region."

The message could hardly have been clearer. US allies in the region -- but especially Taiwan, South Korea, and Japan -- are already nervous about China's regional ambitions, in the knowledge that there are valuable mineral resources waiting to be exploited in the East and South China Seas. That's why they want a beefed-up US military presence.

When I was in China just over a year ago, I was astounded at the huge changes in the country since my previous visit some five years earlier. It wasn't just the rush-hour traffic jams in Beijing; it was also the palpable sense of a society on the move, economically, socially and politically.

No more Communist party minders for visiting foreign journalists; lively political debates on the internet; openly expressed disagreements about some aspects of foreign and economic policy. (No, I'm not saying China has turned into a liberal democracy, far from it -- the Tibetans know that only too well, as do any number of political dissidents and activists -- but there is a far greater degree of political openness than many outsiders appreciate.)

For Mr Xi, it means a country that will be much more difficult to control. An internationally-publicised village rebellion in the south of the country has led to a fascinating experiment: a genuine, open, free election, conducted by secret ballot, in which villagers will be able to choose their own leaders. Perhaps it's a sign of things to come.

For now, though, Western leaders still seem to be fixated on telling China what they want from it. Vote with us on a Syria resolution at the United Nations; free up your trade policies; allow your currency to increase in value so that your competitive advantage is reduced.

But President-to-be Xi is giving little away. In the US this week, he has said nothing that hasn't been said many times before by other Chinese leaders. But he is still the man to watch -- because before too long, he's likely to be the leader of the most powerful nation in the world.

Yes, I know, the question has been asked repeatedly over the past few years -- but I'm afraid it's time to ask it again.

As my colleague Mark Mardell, the ´óÏó´«Ã½'s North America editor, put it in a blogpost a couple of days ago: "The drumbeat of war has grown louder in the past few days."

That drumbeat emanates from Israel, where the defence minister, Ehud Barak, talks of Iran soon entering a "zone of immunity", in other words a moment when its uranium enrichment programme will be so well protected in deep underground bunkers that it will become virtually impregnable.

According to the , the US defence secretary Leon Panetta "believes there is a strong likelihood that Israel will strike Iran in April, May or June ... Very soon, the Israelis fear, the Iranians will have stored enough enriched uranium in deep underground facilities to make a weapon -- and only the United States could then stop them militarily."

And the reported this week: "Amid mounting tensions over whether Israel will carry out a military strike against Iran's nuclear program, the United States and Israel remain at odds over a fundamental question: whether Iran's crucial nuclear facilities are about to become impregnable."

Yes, says Mr Barak; No, say the Americans. The Washington view is that the ever tighter sanctions imposed on Iran are having a real effect, so the best policy is to let them bite harder. The Israelis say they can't risk waiting much longer.

For several decades now, a vital element in Israel's security strategy has been its status as the only nuclear power in the Middle East. (It has never admitted as much, but it's perfectly happy for everyone else to say so.)

But if Iran were to become the region's second nuclear-capable power, that invaluable strategic superiority would be wiped out at a stroke. Israel would, in theory, then itself be vulnerable to a nuclear attack.

Iran, of course, sees things exactly the other way round. It has had nuclear ambitions since the days of the Shah, and no Iranian politician, not even the reformists like Mir-Hussein Moussavi, is prepared to give up Iran's right to develop a nuclear programme, officially solely for peaceful use.

Iranians remember a glorious past when the Persian empire stretched right across the region and included what is now Israel. (Just a few days ago, the deputy Israeli prime minister said he believes Iran is now trying to revive that former empire.)
But imagine you were an Iranian strategic planner. You have recently gained valuable extra regional influence with the US-engineered overthrow of your old enemy Saddam Hussein in neighbouring Iraq, and the installation in Baghdad of a much more friendly, Shia-dominated government.

But to your west, the signs are a lot less encouraging. Your long-time allies in Syria are in deep trouble, and if they are defeated, their place will be taken by a Sunni-dominated administation with no great love for Tehran.

Coming after a string of Arab upheavals that have vastly increased the influence of the Sunni Muslim Brotherhood across the region (aided and abetted by the unimaginably wealthy Qataris), the overthrow of the Assad dynasty in Damascus would be extremely bad news.

So, as you analyse the rapidly shifting power relationships, would you be in the mood to give up a nuclear programme that earns you the attention -- and yes, the fear too -- of your neighbours?

Iran's leaders are not, as the Americans would say, in a good place. The man in charge, the supreme leader Ayatollah Ali Khamenei, is elderly and said to be in poor health. He has fallen out with the president, Mahmoud Ahmadinejad, who is now said to wield little real power.

The economy is in a mess, and many poorer Iranians are finding it increasingly difficult to make ends meet. Uncertainty beyond the country's borders is matched by growing restiveness at home.

According to the : "US officials don't think that [Israeli prime minister] Netanyahu has made a final decision to attack, and they note that top Israeli intelligence officials remain sceptical of the project. But senior Americans doubt that the Israelis are bluffing. They're worrying about the guns of spring -- and the unintended consequences."

Do the names Ian Sartorius-Jones and Gajbahadur Gurung mean anything to you?

Probably not, unless you knew them or their families personally -- but they both died in Afghanistan last week while serving with the British army.

They were the 396th and 397th British service personnel to die in Afghanistan since the anti-Taliban invasion of 2001 -- so the likelihood is that within the next few weeks, the death toll will reach 400.

Now cast your mind back to June 2010. That's when the British military death toll in Afghanistan reached 300. David Cameron had been prime minister for barely a month, and he said this: "We are paying a high price for keeping our country safe, for making our world a safer place, and we should keep asking why we are there and how long we must be there."

What do you think he meant by the words "keeping our country safe ... making our world a safer place"?

This is what I think he meant: defeating the Taliban and al-Qaeda, or at the very least weakening them to such an extent that they pose only a minimal threat.

But now consider that leaked NATO report, based on interviews with thousands of alleged Taliban detainees, which made the headlines this week: "Afghan civilians frequently prefer Taliban governance over the Afghan government, usually as a result of government corruption."

What's more, it suggested there has been "unprecedented interest, even from members of the Afghan government, in joining the Taliban cause."

If you were listening to the programme on Wednesday evening, you'll have heard the former Afghan presidential candidate Ashraf Ghani and the Conservative MP Rory Stewart both agreeing that the only hope for the future of the country is to bring at least some of the Taliban back into the mainstream political process.

In which case, if you were the parent or relative of a member of the British armed forces in Afghanistan, you might be tempted to ask: "Excuse me, Mr Cameron, if the Taliban are on their way back anyway, why exactly are we still sending servicemen and women into harm's way?"

The current plan is for "substantial numbers" of British troops to start withdrawing from Afghanistan next year, and for all combat troops to be gone by the end of 2014. The word yesterday from Downing Street was that the 9,000-strong UK contingent will have ended their lead combat role by the end of next year.

And the Americans are now signalling that they hope to have had made a transition from combat to training and advice by the end of next year as well -- that's rather sooner than they'd previously envisaged -- with more than 20,000 of the current 99,000 US troops in the country having returned home by the end of 2013.

So here's the picture: by the end of next year, substantial numbers of US and British troops will have left Afghanistan. And Taliban commanders, in the words of the leaked NATO report, "increasingly believe their control of Afghanistan is inevitable."

Their confidence may, of course, be misplaced. And it is certainly arguable that by maintaining military pressure on them, the US and its allies will make the Taliban more prepared to engage in a genuine political dialogue.

Meanwhile, there's still the Pakistan issue to be dealt with -- to quote that NATO report again: "Reflections from detainees indicate that Pakistan's manipulation of Taliban senior leadership continues unabated."

Pakistani officials repeatedly deny that they maintain close covert links with the Taliban, but Western intelligence agencies are convinced that, as David Cameron put it 18 months ago, Islamabad is "looking both ways" in the fight against terrorism.

Perhaps it's worth bearing this in mind, though. When Pakistani officials talk of the Taliban, they're thinking principally of the Pakistani Taliban, not the Afghan variety. (Taliban, by the way, simply means students, a reflection of the movement's origins in the religious schools, or madrassas, that were attended by tens of thousands of Afghan refugees who fled to Pakistan after the Soviet invasion of 1979.)

The Afghan Taliban, if the Western spooks are right, are largely guided and run by Pakistani military intelligence. Their Pakistani namesakes, on the other hand, devote much of their time to attacking that same Pakistani military.

According to a analysis: "They share an ideology and a dominant Pashtun ethnicity, but they have such different histories, structures and goals that the common name may be more misleading than illuminating."

None of which, I suspect, will be of much comfort to the British troops on the front line.