NATO leaders raised the Swedish flag on Monday outside their headquarters in Brussels. They took part in a ceremony cementing Sweden's place as the 32nd member of the alliance.

Swedish leaders saw Russian forces invade Ukraine two years ago and concluded membership was the "only reasonable choice." They, and their neighbors in Finland, put aside generations of neutrality in their bids to join. The Swedes had to overcome some resistance from leaders in Turkey and Hungary. But, after waiting 18 months, they saw their country join the bloc last week at a ceremony in Washington.

Prime Minister Ulf Kristersson said Swedes had been preparing "for decades." "We have chosen you and you have chosen us," he said.

Secretary General Jens Stoltenberg welcomed them into the alliance and reminded them of the importance of defending Ukrainians. "President Putin started this war and he could end it today," he said. "Ukraine does not have this option, surrender is not peace."

Swedish troops have already joined their comrades in NATO's largest exercise in decades. About 90,000 personnel will train together to demonstrate their ability to reinforce their "defense of Europe."