It's almost two years since British Forces pulled out of Helmand. I watched them leave. At the time we were told by both politicians and senior military officers that the Afghans were ready to take care of their own security. Hindsight proves they were wrong.

When he announced the drawdown, David Cameron declared it "mission accomplished". But the new Afghan commander in Helmand, General Moen, clearly doesn't agree.

He mentions the attack on the former British base, Camp Bastion, just weeks after the British and US Marines left and then pointedly asks me: "Do you think they completed their mission?"

At the end of last year there were real fears that Helmand would fall to the Taliban. The Afghan security forces were severely tested and in the words of one senior US Army officer "they had their asses kicked".

Another US military adviser described them as a "sucking chest wound", suffering casualties, desertions and corruption. Towards the end of last year, the Afghan Army in Helmand was down to a third of its strength.

Image caption The former British base in Helmand, Camp Bastion, is now deserted

So bad was the situation that last December coalition forces went back in. Initially it was only a handful of British Army trainers, known as "The Helmand 10", but it appears only the Americans were willing to take on the much larger task of rebuilding the Afghan army.

A total of 500 soldiers from the US Army's 10th Mountain Division went into Helmand early this year - a return that took courage.

They occupy a tiny corner of Camp Bastion. Pretty much everything - tents, generators and toilets - has been scavenged from the old base which is now a ghost town. The one new addition is a declaration of intent painted on their front gate: "Reinforce the line - because Helmand can't fall."

The US commander, Brig Gen Andrew Rohling, says they're making "slow and steady progress". I remember the British using similar phrases too. But there is no doubt that the US troops are helping to rebuild the Afghan Army.

Image caption The Afghan Army has been involved in fierce fighting with the Taliban since the British left

The key, says Gen Rohling, has been sorting out leadership and logistics. Providing the Afghans with their own aircraft has helped a bit, too.

Gen Rohling won't criticise those who made the decision to leave Helmand in 2014. He says if it wasn't for them "we'd be starting from zero". Nor does he believe the sacrifices of troops were in vain. Most of the 456 British soldiers who lost their lives in Afghanistan were killed in Helmand.

But he concedes that some of the assumptions made about the strength of the Afghan Army in 2014 might have been wrong.

Many of Helmand's problems are depressingly familiar. The Taliban still hold sway in the same places they fought the British and US Marines: Sangin, Musa Qala and Marjah.

The drugs trade is still booming and no longer is there any idealistic talk of tackling poppy production. Helmand's new governor, Hayatullah Hayat, is the new broom brought in to clean out corruption.

Image caption US troops are now training the Afghan Army in Helmand

He has an unenviable task, but he says there is "hope" with the return of the international community, although he also believes the British left too soon.

The threat hasn't gone away. Not just in Helmand, but across the whole of Afghanistan. Last year the Afghan government lost territory to the Taliban. Its security forces suffered 20,000 casualties, including 5,000 killed, and this year there are fears those figures will be even higher.

And yet the Nato spokesman for the Operation Resolute Support, Brig Gen Charles Cleveland, still says there is reason for "cautious optimism". The Afghan Army "did not break" and that this summer they are conducting offensive operations.

But for Afghanistan the most positive news has been the promise by allies not to quit. President Obama has shelved plans to drawdown US forces to 5,500.

Britain's military commitment will go up to 500 troops, though they'll all be in Kabul. Progress in Afghanistan appears to move at a glacial pace, but Helmand shows that, without international support, it can unravel as fast as lightning.