The American missile strikes that targeted a Syrian military airbase last week, presented as punishment for the use of chemical weapons by the Bashar al-Assad regime, were an unexpected move by the new administration under the leadership of President Donald Trump. They signalled a shift in US policy towards Syria from one of no direct intervention to the opposite.

The strikes were followed up by the announcement that UK Foreign Secretary Boris Johnson's planned trip to Russia had been postponed and a call by Johnson to G7 countries to impose further sanctions on Russia and Syria as a response to Assad's use of chemical weapons.

Western foreign leaders at the G7 summit have reignited debate on regime change in Syria. These developments beg the question of why it is only now that the West is speaking up about action on Syria. The answer to this question lies in Washington.

The Syrian conflict has been grinding on for more than six years with no clear end in sight. Despite multiple ceasefire agreements and several rounds of peace talks, there has not been evidence of political will in the West to bring the conflict to a close.

The main culprit over those years has been the United States. Under former President Barack Obama, the American administration's loudest voice was the White House rather than the State Department or the Pentagon. And the White House's — specifically the president's — position on Syria was to steer clear from military intervention in any way. But it was also one of only paying lip service to political transition in Syria.

All this let the Syrian conflict continue, and this was not helped by the United States' approach to the conflict that was built on not allowing any one side to win militarily.

This approach was taken on the basis that if neither the regime nor the opposition rebels feel they could win, then both would be forced to the negotiating table. Instead of being forced to negotiate, not winning militarily — coupled with continued funding from foreign backers on both sides — meant that both the Syrian regime and the rebels continued to try to achieve a military victory.

Although the United Nations called for talks, the UN proved to be largely incapable of effecting change on the ground. Russia regularly vetoed Security Council resolutions.

Most humanitarian aid channelled through the UN ended up in regime areas, not opposition areas. And talks in Geneva were used as an opportunity by the Syrian regime and Russia to simply badmouth and undermine the opposition instead of engage in actual negotiations. The United States took part in the peace talks but without playing a leading role.

It was as if the United States had taken a vow of silence in order to prove that President Obama meant it when he said that he would not be dragging the United States into another quagmire in the Middle East in the aftermath of the Iraq intervention of 2003.

Obama's policy meant that the US did not display political leadership on the Syrian issue, leaving that role wide open to Russia, which used the Syrian crisis as a convenient way of asserting itself in the face of the United States.

When Trump came to power, there was much focus on his relationship with Russia, seen as much warmer than that of his predecessor. But no matter how soft Trump is on Russia, he cannot afford to be seen as the president who allowed Russia to become a superpower rivalling the United States. And he also wanted to prove that, unlike Obama, he means what he says.

The significant number of former advisors to Obama who have praised the missile strikes ordered by Trump shows how much of an influence Obama himself had on the way the United States government handled Syria.

With things stirring in Washington, the rest of the West woke up from its slumber. This illustrates very clearly the importance of American political will and its influence on Western policy.

The challenge right now for the Trump administration is to follow up its isolated military action with a comprehensive strategy for ending the Syrian conflict. If this strategy is designed in Washington, building a Western alliance to support it will not be a hurdle. The hurdle lies in whether or not the United States is going to play a leading diplomatic as well as military role to pave the way for political transition in Syria.

Lina Khatib is the head of the Middle East and North Africa Programme at Chatham House