What did the United States prevent Red China from joining?​

The United Nations.

Explanation:

(This was the US's policy from the founding of the UN until 1971, when the US changed its policy and voted to seat the People's Republic of China ("Red" China) and expel Taiwan from the UN.)

lincoln presided over the union victory in the american civil war, which dominated his presidency. a former whig, lincoln ran on a political platform opposed to the expansion of slavery in the territories. his election served as the immediate impetus for the outbreak of the american civil war.