But the Kosovo campaign can still be instructive in other respects because it offers lessons on expecting the unexpected and on improvising in the midst of a confrontation.

As in the case of Syria today, there was no United Nations resolution explicitly authorizing NATO to bomb Serbia. But NATO nations found other ways, including an earlier U.N. Security Council Resolutionpage 105, to legally justify what had to be done. In Syria, the violation of the 1925 Geneva prohibition against the use of chemical weapons is probably sufficient justification. (The fact that Russia used chemical weapons in Afghanistan in the 1980s should be used to undercut Russian objections to strikes against Syria today.)

Kosovo also reminds us that it isn’t imperative to strike back immediately after a “red line” is crossed. In 1998, NATO had established a red line against Serb ethnic cleansing; the Serbs crossed that line with the massacre of at least 40 farmers at Racak in January 1999. But NATO didn’t strike immediately. Instead, France took the lead for a negotiated NATO presence. This strengthened NATO’s diplomatic leverage and legitimacy, even though the talks failed.