It's not particularly unique that someone who you see as an ally at one point is an enemy a short while later. Britain and France were on the brink of declarin

It's not particularly unique that someone who you see as an ally at one point is an enemy a short while later. Britain and France were on the brink of declaring war to USSR (then an ally of Nazi Germany) in 1940. Sixteen months later in mid-1941, they were allies with USSR in war against Germany, until 1945. And then the Iron Curtain fell, and just four years later NATO was formed to again counter the threat from USSR. Such changes are in no way restricted to late 20th century.