"The reason why Britain didn’t declare war on the Soviet Union is an
intriguing one. Unknown to the general public there was a ‘secret
protocol’ to the 1939 Anglo-Polish treaty that specifically limited the
British obligation to protect Poland to ‘aggression’ from Germany" http://www.historyextra.com/qa/why-did-britain-and-france-not-declare-war-soviet-union-when-red-army...
Overestimate one’s capabilities, to be overly confident is harmful
Many people/groups were involved. Anti-war marches and other protests, such as the ones organized by Students for a Democratic Society (SDS), attracted a widening base of support over the next three years, peaking in early 1968 after the successful Tet Offensive by North Vietnamese<span>troops proved that war's end was nowhere in sight. I mean, who wouldn't be mad? There was a draft that forced citizens to fight in a war they didn't even believe in! A war that lasted 19 YEARS and 180 days!
Since there's too many people/groups to put here, go to this website and see the full list: </span>https://en.wikipedia.org/wiki/List_of_anti-war_organizations
Hope this helps!!