Patrick, a Romano-British former slave turned bishop, spent decades evangelizing Ireland after escaping captivity there as a youth. His death, traditionally dated to this day, became the basis for the feast day that later evolved into a global celebration of Irish identity, from Dublin parades to green rivers in Chicago.

After wars against Austria and a campaign of diplomacy and conquest led by Camillo di Cavour and Giuseppe Garibaldi, the various Italian states—kingdoms, duchies, and papal territories—were consolidated under the House of Savoy. Rome and Venice remained outside the new kingdom, added only years later, but the proclamation marked the effective birth of the modern Italian state.

Ten days after the Soviet-backed communist coup in Czechoslovakia, Truman told a joint session of Congress that the world faced a stark choice between freedom and dictatorship. His speech accelerated Cold War military buildup and helped pave the way for the Selective Service Act's renewal that June.

Commander James McDivitt, along with David Scott and Rusty Schweickart, tested docking, undocking, and rendezvous maneuvers between the command module and the lunar module 'Spider,' proving the hardware needed for a Moon landing worked as designed. The mission's success cleared the way for Apollo 10's dress rehearsal and, four months later, Apollo 11.