Is it true that . . .   women in the United States were not guaranteed the right to vote until 1920?

The answer is yes. While some states did allow women to vote before the passage of  the 19th Amendment to the Constitution, the right to vote for women in the United States became official on August 26, 1920.

The facts: Voting is a matter for state laws except when the Constitution sets a specific mandate for federal electors. Nothing in the U.S. Constitution forbid women from voting, but it did not require voting equality by sex until the 19th Amendment. Before then, some western states began permitting women to vote and hold office, state and federal. (Jeannette Rankin was elected to the House of Representatives from Montana in 1916.)

In the 19th century, women seeking the right to vote lectured, wrote, marched, and lobbied to gain support for woman suffrage. Initially considered a radical idea, and despite significant resistance, suffragists lobbied on both the state and national level for years. Legislation was regularly introduced in Congress and repeatedly defeated from 1880 until 1919.  

Legislation leading to the 19th Amendment was first introduced in the House during a special session of Congress on May 19, 1919.  H.J. Res.1 passed the House on May 21 after a day of debate. The resolution was then sent to the Senate for consideration. The Senate debated the resolution on June 3 and finally passed it on June 4. Following House and Senate passage, the constitutional amendment was sent  to the states for ratification. After nearly a generation of struggle, the 19th Amendment granting  women the right to vote became part of the U.S. Constitution on August 26, 1920.