Religion was just an excuse for warfare. The most dangerous and in terms of body count, ideas have all come from the Left. Communism / Socialism has killed somewhere north of 250 million people just in the 20th Century alone. The most successful empires weren't based on religion either:
Mongol
Roman
Byzantine
Greek (Alexander)
Persian
Hittite
To name a few.
World Wars 1 & 2 were not fought for the causes of communism or socialism or religion.
The escalation of hostility in Vietnam was caused by a capitalist country trying to stem the spread of socialism and Communism.