Why did nationalism became popular in 1945?

Nationalism became popular in 1945 because of the weaknesses of the British and French positions due to WWII.  The Vietnamese under Ho Chi Minh felt as though they should be rewarded for fighting against the Japanese during the war.  They resisted French efforts to bring them back under colonial rule and finally pushed the French out in 1954.  India became a nation after WWII after resisting British rule for decades.  In 1945 Jewish nationalists started to argue for a homeland in the Middle East--their arguments were strengthened by the atrocities committed during the Holocaust.  The formation of Israel in 1948 was the result of decades of arguments for creating a Jewish homeland.  Nationalist movements also sprang up in Eastern Europe as a response to Soviet control.  After WWII, Soviet soldiers fought against the same Baltic partisans who helped them defeat Hitler.  There were also resistance movements in Hungary and Poland against Soviet control--these were quickly and ruthlessly put down.  Just like after WWI, nationalism became very important after WWII as marginalized people sought to take control of their own affairs.  In some cases they were successful.