Israel. They defeated much more numerous opponents quite easily.

The Chineses did not perform very well. They almost conquered Korea, but they were more than 1 million, much more than the UN (US and South Korea army), and in the end, they got heavily defeated until the Pam Mun Jong treaty.
They also lost their war against USSR and perhaps against India (not too sure about the last one). Invading Tibet is not a big achievement, since Tibetains mostly did not fight back.



Followed by successful (somewhat) Peacekeeping missions in Bosnia and Kosovo.
Wait, I thought Russia, France, Germany and UK were part of these missions, no ?