Celebrate the fall of the ISIS caliphate, but remain vigilant

The last malignant cells of a terror caliphate that once sprawled from Syria to the gates of Baghdad were vanquished over the weekend. But like any cancer that can re-emerge in the absence of therapeutic vigilance, the Islamic State is only now in remission.

The destruction, after five years, of a movement that once controlled an area of Syria and Iraq about the size of Maine is a victory for civilization over barbarity. Both the Obama and Trump administrations can take credit. President Barack Obama, whose withdrawal of U.S. troops from Iraq created a vacuum for the Islamic State to fill, launched the multinational anti-ISIS campaign, and President Donald Trump continued and accelerated it.

The American military, armed with hard-earned lessons from long and costly conflicts in Iraq and Afghanistan, was the architect of this success. A U.S.-led air campaign — joined by Britain, France, Jordan and other allies — carried out thousands of airstrikes. On the ground, U.S. special forces assisted Iraqi security troops and Kurdish fighters in liberating Iraq's second largest city of Mosul in 2017. American forces also embedded with Syrian Arab and Kurdish gunmen who captured the Islamic State capital of Raqqa in Syria that same year. After that, the caliphate's demise was a matter of time.

The United States spent $28.5 billion during five years of fighting the caliphate, a fraction of the $1.5 trillion cost of American wars against terrorism since 9/11. Where thousands of U.S. troops died in Iraq and Afghanistan, 16 were killed in action against ISIS.

It was hardly a bloodless war. More than 20,000 U.S.-allied fighters on the ground in Iraq and Syria were killed, along with estimates of 70,000 Islamic State militants. Vast sections of Mosul, Raqqa and other embattled cities were left in ruins.