Whom did the US indirectly declare war against when they declared war against Britain?

How did the Americans faired early in the war of 1812?

Why were the British able to send more forces after the spring of 1814?

To answer the first question, the US indirectly declared war against Spain as well when they declared war against Britain.

For the second question, the Americans were doing really well early in the war.

Until the British won the war against Napoleon in the spring of 1814, which has allowed them to send more forces to the United States.