Of course, the major effect of the Louisiana Purchase was that it made the United States much bigger than it had been before. The Purchase doubled the land area of the country. This helped to make Americans feel like their country was strong and important, contributing to a sense of nationalism.
Americans were unfamiliar with the territories of Vietnam and ended up having to search manually, house by house, allowing the Viet Cong to dig escape tunnels and snipe American soldiers.
D. Remained poor.
They experienced a period of economic stagnation following the independence. Making a lot of people remained poor despite being free from the European colonization. They need some time before they eventually make adjustments to implement a proper political system in place and develop their economy.