The Zimmerman Telegram suggested that Mexico ally itself with Germany against the United States. What did the telegram convince Congress to do?

invade Mexico

give back Texas, New Mexico, and Arizona to Mexico

declare war on Germany

ask that the United States ally itself with Germany

It convinced congress to declare war on Germany

The Zimmerman Telegram was one of the key reasons the United States declared war on Germany.

The Zimmerman Telegram was intercepted by the British and passed along to the Americans in mid-January 1917. On April 2, 1917, the United States congress declared war. But the Zimmerman Telegram was not the only reasons the US joined the war.

Have you ever heard of the Lusitania? It was a luxury cruise ship that was sunk by a German submarine in May 1915, killing 128 Americans. But these two issues were not even enough to convince the Americans to declare war on Germany.

The final straw was when the Germans began to sink US merchant ships. After the sinking of Lusitania, Germany had promised to only sink ships that were enemy ships or carried weapons or military supplies. On January 31, 1917, Germany began to start sinking United States merchant ships again. This made the Americans push for war.

The Zimmerman Telegram, the sinking of the Lusitania, and the attack on the United States neutral merchant ships all led to the United States entering World War 1.