After Rambouillet, the US and NATO never claimed the right to send armed forces into Yugoslavia unless invited to do so by its government. They did, however, assert the right to launch air attacks to extract the invitation. The humanitarian motive the President claims is demonstrably false. The bombing attack caused, rather than prevented, the evacuation of Kosovo Albanians. The only difference is that, rather than going abroad to expand it's power, it is seeking to hold on to the little of its nation that remains.
Some analysts suggest economic motives.
Nothing strikes more terror into the hearts of our bipartisan political oligarchy than this prospect. No external enemy poses a threat to it. The only threat comes from inside, from the American people, who alone are capable of depriving our rulers of their power to rule over us. When Americans started once more to demand democratic reform, the progressive movement was killed off by US intervention in World War I and dissent ruthlessly suppressed by police state methods. When during the Great Depression, Americans demanded that their government address their needs, the government was obliged to grant some reforms.