BAGHOUZ, Syria (AP) — U.S.-backed forces declared military victory over the Islamic State group in Syria on Saturday after liberating the last pocket of territory held by the militants, marking the end of a brutal self-styled caliphate the group carved out in large parts of Iraq and Syria in 2014.

The nearly five-year war that has devastated cities and towns across north Syria and Iraq ended in Baghouz, a minor border village where the cornered militants made their last stand, under a grueling siege for weeks.

On Saturday, the Syrian Democratic Forces raised their bright yellow banner from a s...