United States air strikes in Iraq from 8 August and Syria from 23 September may have slowed up Isis advances and inflicted heavy casualties on its forces in the Syrian Kurdish town of Kobani. But Isis has its own state machinery and is conscripting tens of thousands of fighters to replace casualties, enabling it to fight on multiple fronts from Jalawla on Iraq’s border with Iran to the outskirts of Aleppo in Syria.

In western Syria, Isis is a growing power as the Syrian government of President Bashar al-Assad loses its advantage of fighting a fragmented opposition, that is now uniting under the leadership of Isis and Jabhat al-Nusra, the Syrian affiliate of al-Qaeda.

Yet it is only a year ago that President Obama dismissed the importance of Isis, comparing it to a junior university basketball team. Speaking of Isis last January, he said that “the analogy we use around here sometimes, and I think it is accurate, is if a JV [junior varsity] team puts on Lakers uniforms it doesn’t make them Kobe Bryant [famed player for the Los Angeles Lakers basketball team].” A year later Obama’s flip tone and disastrously inaccurate judgement jumps out at one from the page, but at the time it must have been the majority view of his national security staff.

Underrating the strength of Isis was the third of three great mistakes made by the US and its Western allies in Syria since 2011, errors that fostered the explosive growth of Isis. Between 2011 and 2013 they were convinced that Assad would fall in much the same way as Muammar Gaddafi had in Libya.

Despite repeated warnings from the Iraqi government, Washington never took on board that the continuing war in Syria would upset the balance of forces in Iraq and lead to a resumption of the civil war there. Instead they blamed everything that was going wrong in Iraq on Prime Minister Nouri al-Maliki, who has a great deal to answer for but was not the root cause of Iraq’s return to war. The Sunni monarchies of the Gulf were probably not so naïve and could see that aiding jihadi rebels in Syria would spill over and weaken the Shia government in Iraq.

How far has the political and military situation changed today? Isis has many more enemies, but they remain divided. American political and military strategies point in different directions. US air strikes are only really decisive when they take place in close cooperation with troops on the ground. This happened at Kobani from mid-October when the White House decided at the last minute that it could not allow Isis to humiliate it by winning another victory. Suddenly the Syrian Kurdish fighters battling IS shifted from being “terrorists” held at arm’s length to being endangered allies. As in Afghanistan in 2001 and in northern Iraq in 2003, experienced personnel in the front line capable of directing the attacks of aircraft overhead are essential if those strikes are to be effective.

When the bombing of IS in Syria started, the government in Damascus felt that this was to its advantage. But while the US, Arab monarchies, Syrian rebels and Turkey may have overplayed their hands in Syria between 2011 and 2013, last year it was the Syrian government that did the same thing by seeking a solely military solution to the war. It has never seriously tried to broaden its political base at home by credible offers to share power, relying instead on its supporters to go on fighting because they believe that anything is better than a jihadi victory. But these supporters are becoming worn out by the struggle because they see no end in sight.

The government has always been short of combat troops, a weakness becoming more apparent as it calls up more reservists and diverts conscripts from entering the National Defence Force militia into the regular army. Government forces have made gains around Aleppo and Damascus, but they are losing ground south of the capital and in Idlib province.

There have always been political advantages for Assad at home and abroad in having the Syrian rebels dominated by “terrorists” of whom the West is frightened. But the dominance of Isis and Jabhat al-Nusra means that the Syrian army is losing its advantage of being a single force facing a disunited foe with 1,200 different factions. A sign of this underlying weakness is the failure of government troops to launch an expected offensive to retake rebel held parts of Aleppo.

Isis won great victories in Iraq in the course of the year by taking advantage of the alienation of the Iraqi Sunni Arab community. This tied the Sunnis’ fortunes to Isis and, while they may regret the bargain, they probably have no alternative but to stick with it.

The war has become a sectarian bloodbath. Where Iraqi army, Shia militia or Kurdish peshmerga have driven Isis fighters out of Sunni villages and towns from which civilians have not already fled, any remaining Sunni have been expelled, killed or detained. Could Isis launch another surprise attack as in June? This would be difficult outside Sunni-majority areas, though it could provoke an uprising in the Sunni enclaves in Baghdad, probably with disastrous results for the remaining Sunni in the capital. They were forced out of mixed areas in 2006 and 2007 and mostly confined to what a US diplomatic cable at the time called “islands of fear” in west Baghdad. Isis could create mayhem in the capital, but the strength of the Shia militias is such that it would probably be at the price of the elimination of remaining Sunni enclaves.

Syria’s two main foreign backers, Russia and Iran, are both suffering from the collapse in the oil price. This may make them more open to a power-sharing compromise in Syria, but it is by no means clear that they are being offered a deal by the West and its Arab allies. This may be a mistake since at the end of the day the great confrontation between Sunni and Shia across the Muslim world is not going to be decided by Iranian or Russian budgetary problems. Iraqi Shia militia units that withdrew from Syria to fight Isis in Iraq can always be sent back and reinforced.

The Iranians really do feel this is a war they cannot lose whatever the impact of economic sanctions imposed by the US. The balance of power between government and Isis looks fairly even in Iraq at the moment, but this is not true in Syria where Sunni Arabs are 60 per cent of the population as opposed to 20 per cent in Iraq. Above all, Isis is strengthened in Syria by the fact that the West, Turkey and the Sunni Arab states are seeking the fall of Assad, Isis’s main opponent, as well as the overthrow of Isis itself.

The mutual hatreds of its enemies remain Isis’s strongest card.