During the breakup of Yugoslavia, the United States engaged in both combative and economic conflict, particularly with Serbia, known at the time as the Federal Republic of Yugoslavia (one of socialist Yugoslavia's successor states). The United States imposed sanctions and spearheaded a NATO bombing campaign against Yugoslavia in 1999. During this period, another wave of Serbian emigration ensued, and many Serbian refugees moved to the United States. In the 2000s, diplomatic relations between the United States and Yugoslavia were restored, but were changed when Montenegro seceded in 2006, after which Serbia was the successor state to continue relations previously held by the Federal Republic of Yugoslavia. Kosovo unilaterally declared independence from Serbia in February 2008, a move which the US recognized.