While an ardent believer in Comunism, he was fundenentally a nationalist first and foremost. He was absolutely pragmatic in his approach to politics and playing his hand. While this is best evidenced by his approach to the Sino-Soviet split and his strategy in the Vietnam war, his earlier exploits bear significant similarities with his later ones.

Key to this question was his behavior during Japanese occupation. Ho Chi Minh led the resistance fighters in Indochina against the Japanese. He was well liked by his troops as well as his American supporters. His US contacts were firm in their support for Vietnamese Independence and assured him that he had the US' support.

And in a way, he did. FDR was vocal in his support for Nationalist movements and decolonization. He vocally supported the Independence of other countries in the region, notably the US' own colony, the Philippines. While FDR never spoke about Vietnam, it is likely he would have at least given it lip service.

When the war ended, Minh declared independence. The declaration was given with the support of US special forces who were in attendance and was styled after the US' own declaration. However the post-WWII climate was far different. The US under Truman was operating under different principles all together.

Colonialism may have been a primary concern before the Second World War, The political concerns after fell to the reconstruction of Europe and the containment of the USSR. In France, DeGaulle saw rebuilding the French empire as an absolute necessity and maintaing control of colonies as paramount. His relationship with the US was rocky at this point, but the US saw Europe as the next potential battleground and wished to maintain their allies there. Because of this, they didn't place pressure on the colonial powers to decolonize and even assisted in their efforts to keep them.

During this time, Ho Chi Minh requested US support, but recieved no response. By 1950 the US was actively supporting France and Minh sought support from Stalinist Russia and Maoist China. Still, following the French withdrawal and before the escalation of condlict, he remained willing to compromise with the US and sent many messages offering compromise, but these were rejected by the US under the containment theory of politics embraced by politicians in the US and other capitalist countries.

South Vietnam had a nominal democracy, but was in reality a US backed dictatorship led by their chosen candidate, Ngo Dinh Diem. While reunification elections were called for and agreed upon, the realpolitik of the Western powers prevented them from ever really happening.

Again, Ho Chi Minh was a communist, but he was a Nationalist before anything else. He wanted Independence for Vietnam and was happy to have the US' support when they seemed like the strongest ally.

Sources

America's Longest War , George Herring

A Vietnam War Reader, ed. Michael Hunt

Ho Chi Minh: A Life, William Duiker

Vietnam: the Definitive Oral History, Christian Appy