Tucker Carlson: NATO is not a defensive alliance - who did Yugoslavia attack?

American journalist Tucker Carlson used the example of Kosovo's secession from the Federal Republic of Yugoslavia to prove to journalist Piers Morgan that NATO is not a defensive alliance.
"Where were you when there was a war in Yugoslavia and when they bombed Christians in Yugoslavia? Do you remember that, that was quite offensive," Carlson asked Morgan in an interview published on the American journalist's website.
Carlson was responding to Morgan's claim that "NATO has never acted unilaterally aggressively and has never attacked anyone without being attacked."