# Unrestricted Submarine Warfare (1917)

URL: https://germany-history.com/timeline/1917-unrestricted-submarine-warfare
Location: Atlantic
Categories: main-event

In February 1917 Germany resumed unrestricted submarine warfare. Together with the Zimmermann Telegram, it brought the United States into the war in April 1917. American troops tipped the balance.

## Why it matters
It brought the US into the war against Germany.

Ruler at the time: [Wilhelm II](https://germany-history.com/rulers/wilhelm-ii)

## Sources
- [Wikipedia – Atlantic U-boat campaign of World War I](https://en.wikipedia.org/wiki/Atlantic_U-boat_campaign_of_World_War_I)
- [Wikipedia – Zimmermann telegram](https://en.wikipedia.org/wiki/Zimmermann_telegram)
- [Encyclopaedia Britannica – Zimmermann telegram](https://www.britannica.com/event/Zimmermann-Telegram)