As NATO celebrates its 75th anniversary, tracing back to the 1949 Washington Treaty, the alliance's core principle of collective defense under Article 5 remains pivotal, having been invoked once following the 9/11 attacks. The summit will focus on Ukraine, deterrence, defense, and global partnerships, marking the last for Secretary General Jens Stoltenberg, succeeded by Mark Rutte. NATO, with 32 members, continues to evolve from countering the Soviet threat to addressing contemporary challenges like Russia's actions in Ukraine and global strategic competition.