Tobias Billstrom, Sweden’s foreign minister, has surprised everyone by suddenly resigning from his role and leaving politics entirely. Billstrom, who played a key role in Sweden’s historic move to join NATO, didn’t give any specific reason for his decision. His announcement left the country in shock, especially since he was only 50 years old and had been involved in politics for over two decades.

Billstrom first entered Swedish politics in 2002 when he was elected to parliament. He climbed the ranks and became foreign minister in 2022, where he worked on one of Sweden’s biggest recent political changes—giving up its long-held neutrality and joining NATO. Sweden’s entry into NATO marked a turning point for the country, aligning it more closely with the Western powers and supporting Ukraine in its fight against Russian aggression.

When Billstrom announced his resignation, he did so in a heartfelt post on X (formerly Twitter). He expressed a mix of pride and sadness as he infor...