Diplomatic Victories are won when the game player has all types of alliances with every remaining Civilization.
The year is 1940 and you must do the impossible: play as France and eventually re-occupy dozens of cities before August 1940. And lasts until infinite if this feat is accomplished.
In March 1945, the Allies broke through the Ardennes hills into Germany after the Battle of the Bulge. The French player will need to beat this deadline by just under 5 years. The French civilization has the most treaties at the start, so it's advisable to pick France to occupy all German and German occupied cities. This means you must re-occupy all of Netherlands should Netherlands surrender in first half of May.