On March 12, 1959, Congress approved Hawaii for admission to the union as the 50th state, marking the last time statehood was subject to votes in the House and Senate.

President Dwight Eisenhower signed the Hawaii Admissions Act a week later on March 18, 1959, and Hawaii officially became the 50th state on August 21, 1959, after Hawaiians voted to become a state in June 1959 under terms specified in the Admissions Act.

The Constitution grants general state-creation powers to Congress in Article IV, Section 3, under the Admissions Clause, which reads: “New States may be admitted by the Congress into this Union; but no new State shall be formed or erected within the Jurisdiction of any other State; nor any State be formed by the Junction of two or more States, or Parts of States, without the Consent of the Legislatures of the States concerned as well as of the Congress.”

Since 1789, states have joined the union in various ways. The usual process has been for Congress to grant territorial status as a precursor, with a territory creating a local constitution for its citizens that conforms to the federal Constitution and the Declaration of Independence. In other cases, such as Texas, West Virginia, Vermont and Kentucky, the admission process differed. But since West Virginia’s admission to the union in 1863, the state admission process has been restricted to territories.

On the Interactive Constitution, Eric Biber and Thomas B. Colby describe the general evolution of the statehood process in recent times:

“The Admissions Clause provides that admission of a state requires at least one Act of Congress. However, Congress has often followed a more complicated process. For many admitted states, Congress first passed an Enabling Act, which authorized the population of a territory to convene a constitutional convention to draft a constitution for the new proposed state, and to apply for admission to Congress,” they explain.

“Often in the Enabling Act, Congress specified a range of conditions that the proposed state had to meet in order for admission to occur. … Once the proposed state constitution was drafted, it was sent to Congress, which then decided whether to pass an additional act or resolution admitting the state. One variation in the Enabling Act process involved Congress delegating the final approval process to the President.”

Efforts to add Alaska and Hawaii as states with “an equal footing with the other States” had picked up in their intensity after World War II when the strategic importance of both territories became more urgent. However, politics played a role in the statehood process in a divided Washington.

The admission of a state brings with it new electoral votes and new representatives in Congress. The Democrats during the 1950s favored Alaska as the 49th state, while the Republicans wanted Hawaii admitted by itself, with both sides believing there was a political benefit to the admissions process.

President Eisenhower had publicly supported Hawaiian statehood, but he had not supported Alaskan statehood until 1958 when it became clear that both territories would need to be admitted as states to keep a political balance in Washington.

In January 1959, Alaska became the 49th state, which accelerated the Hawaii statehood process. On March 11, 1959: the Senate voted 75-15 in favor of the Admissions Act, with the House approving the same bill in a 323 to 89 vote on March 12, 1959.

During the 1940s and 1950s, there was also a serious debate about the status of Puerto Rico as a potential state, or as an independent nation. Today, the statehood debate for Puerto Rico remains controversial. There is also a statehood movement in the District of Columbia.