Hungary's parliament on Monday approved Sweden's accession to NATO, clearing one of the final hurdles for the country to join the military alliance.

Why it matters: NATO has been key to the U.S.-led effort to counter Russia's unprovoked invasion of Ukraine, and the defensive alliance has long been central to maintaining security and U.S. interests in Europe.

• Sweden's accession as the 32nd member country of NATO is a blow to Russian President Vladimir Putin. He has said Russia's invasion of Ukraine was at least in part motivated by the Kremlin's desire to halt NATO's eastward expansion.
• Joining NATO ends Sweden's more than 200-year track record of military non-alignment.

Driving the news: Joining the alliance requires unanimous approval from NATO countries. After delaying a decision for more than 18 months, Hungary was the final NATO member left to ratify Sweden's accession.

• Hungarian Prime Minister Viktor Orbán, widely seen as the most pro-Russian leader in the European Union, met with Swedish Prime Minister Ulf Kristersson last week. Orbán ultimately endorsed the accession after Sweden agreed to send Hungary fighter jets.
• Orbán told Hungary's parliament Monday that the arrangement would strengthen its security. "Therefore, I ask my fellow lawmakers to approve the legislation on Sweden's NATO accession in a vote today," Orbán said, per Reuters.

What they're saying: "Sweden stands ready to shoulder its responsibility for Euro-Atlantic security," Kristersson said on social media, calling the day "historic."

• "Sweden's membership will make us all stronger and safe," NATO Secretary General Jens Stoltenberg said on social media after commending the Hungarian parliament for its vote.
• "Now that all Allies have approved, Sweden will become the 32nd [NATO] Ally," he added.

Flashback: Both Sweden and Finland applied to join NATO in May 2022 in the wake of Russia's invasion of Ukraine.

• Finland formally joined the alliance last April.
• Ukraine has also lobbied to join the alliance. Kyiv submitted an accelerated membership application in September 2022, but its request has divided NATO members.
• Ukrainian President Volodymyr Zelensky has criticized NATO for failing to provide a concrete timetable for Ukraine's membership.
• President Biden said last summer that it would be "premature" for Ukraine to begin the accession process before the end of the war.

What's next: NATO and Sweden need only compete a few more steps before its accession to the alliance becomes official.

• Stoltenberg will invite Sweden, and Stockholm's government will in turn approve the accession.
• Finally, the accession documents must be formally filed at the U.S. State Department, which serves as the alliance's depositary.

Go deeper: Why NATO formed, why Finland joined and why Sweden wants to join

Editor's note: This story was updated with additional context on the accession process and reaction from leaders.