WASHINGTON — Defying Western efforts to confront the Islamic State on the battlefield, the group has evolved in its reach and organizational ability, with increasingly dangerous hubs outside Iraq and Syria and strategies that call for using spectacular acts of violence against civilians.

But even as the militant attacks were playing out across Paris on Friday night, the United States carried out an airstrike — planned days in advance — against the leader of the Islamic State in Libya, which has emerged as a pivotal stronghold for the group in North Africa. American and British Special Operations forces have for months been conducting secret surveillance missions in Libya to monitor the rise of fighters aligned with the Islamic State.

Read the article “Strategy Shift for ISIS: Inflicting Terror in Distant Lands” on nytimes.com.