Two years into Washington’s war against Islamic State, it may finally be winning. At the same time, however, its influence over events in the broader Middle East seems perhaps terminally in decline.

What happens in the coming months and years in Syria will be key to the future shape of the region. No country has challenged US policy-makers more – and the Obama administration has faced heavy criticism.

This month, however, has seen what feels like the first good news for the United States from Syria since the uprising began.

In early August, US- backed Syrian forces seized back the town of Manbij. Footage of jubilant locals embracing those they see as liberators has been flashed around the globe, providing exactly the kind of propaganda victory Washington needed.

Manbij could open the door for an offensive against the true militant heartlands. Islamic State is losing ground, money and support. It may soon be stripped of remaining strongholds in Raqqa, Syria, and Mosul, Iraq.

But the battle for the future of Syria – and, indeed, the Middle East – is much more complex than the fight against Islamic State. And there are powerful forces – particularly Vladimir Putin’s Russia, Iran and what remains of Bashar al-Assad’s government – that also want to call the shots.

The United States and Europe long struggled to find an approach to Syria, undecided on how hard to push against Assad and how much to back – or trust – the opposition. Moscow, in contrast, has always known which side it was on.

This week, Russia shocked US analysts by moving long-range bombers to Iran, flying through Iraq airspace to strike targets in Syria. It was the first time Iran’s rulers had allowed their military bases to be used by a foreign power at least since the 1979 revolution, a dramatic sign of the growing Russia-Iran axis.

The strikes came against the backdrop of a much broader escalation by the Syrian government and its allies that some reports suggest has included a handful of chemical strikes. In Aleppo, the UN says an upsurge in fighting in recent weeks has killed hundreds and markedly worsened the already catastrophic humanitarian situation.

In many respects, the relatively small town of Manbij is a sideshow compared to some of the larger, longer running battles and sieges. But for the United States, it was a major achievement. The victors were, on paper at least, the “moderate Syrian opposition,” an entity the United States has been desperately hoping would come into existence for years.

Given its unsuccessful and wasteful early attempts at building that opposition, this victory is no small deal.

Complex reality

The reality was always somewhat more complex – according to some accounts, up to 60% of Syrian Democratic Fighters are Kurdish. While the group also includes Sunni and Assyrian fighters, it’s not the kind of pan-Syrian force the West would really like to see. It is, critics say, essentially dominated by the Syrian Kurdish YPD – which means its successes are viewed with suspicion by neighbouring Turkey – no fan of Kurdish separatism – and Iraq.

Whether the United States can grow enough moderate local forces to significantly alter the larger conflict remains unclear. Eventual peace will likely come down to a negotiated deal that must involve both local Syrian actors and their international backers.

The broader geopolitics now seem clear. Moscow has put itself firmly on the side of the Shia-run Tehran-Damascus axis. At the same time, however, the United States is drifting further from its key Sunni regional partners, particularly Saudi Arabia and Turkey.

That’s not necessarily a criticism of President Barack Obama – history handed him a nightmarish situation. The more robust interventionist approach of the George W. Bush administration was no more effective – and in many respects a lot more costly. Obama has had his share of successes, in particular, avoiding war with Iran. Most importantly, the kind of military operation the United States is currently pursuing in the region is much more sustainable.

Broadening US military and diplomatic focus beyond the Middle East was, after all, one of Obama’s earliest ambitions. The United States is much less dependent on Middle Eastern energy. It also has growing responsibilities and worries elsewhere, not least in confronting a rising China and resurgent Russia.

It is in its growing confrontation with Moscow, however, that things get complicated.

In Russia, the United States now faces a rival great power that is willing to take the kind of decisive action to alter the course of events in the Middle East that had previously been limited to Western states.

Neither Moscow nor Washington, it’s clear, have any enthusiasm for the kind of troop-heavy missions the West tried in Iraq and Afghanistan. These are very different conflicts, fought largely by local forces with support and advice from powerful outside sponsors.

Despite what some in the United States might want, there is little appetite in Washington for expanding strikes to deliberately weaken Assad’s forces. Such action might, in any case, merely prolong Syria’s nightmare. Attacking anything belonging to nuclear-capable Russia, of course, is not on the table at all. It would just be too risky.

There’s clearly a significant moral gap between the unrestrained brutality of Putin and Assad and Washington’s more limited approach, moderated as it is by a desire to keep down unnecessary casualties and collateral damage. Still, the West doesn’t have nearly as much moral high ground as it might like to believe. Washington is seen still turning a blind eye to the actions of its allies – for example, in Saudi Arabia’s increasingly bloody Yemen intervention.

Whoever wins the US presidency in November will want to put their own mark on America’s role in the Middle East. Where things stand in Syria when they take office, however, will hugely influence their options.

That means plenty for all sides to fight for in the weeks and months to come. Don’t expect things to get any simpler anytime soon.

[Peter Apps is Reuters global affairs columnist, writing on international affairs, globalisation, conflict and other issues.