6. The Six-Day War (1967)
The Six-Day War erupted on June 5, 1967, when Israel launched a preemptive strike against Egypt, Syria, and Jordan without a formal declaration of war. The conflict was marked by rapid territorial changes, with Israel capturing the Sinai Peninsula, West Bank, and Golan Heights (history.com). The swift and decisive nature of the war underscored the volatility of modern undeclared conflicts.
