[Astromancer]

Extra bays and altered coarses for rivers would lead to some interesting alternate worlds.

Example: Add a sixth Great Lake, Lake Dakota. Lake Dakota would stretch from an inlet at about the Minnesota/Ontario border, to about 175 miles westwest of Homeline's Montanna/North Dakota border. Once the Eire canal opens, large numbers of people form New England and the Middle Atlantic states flood west. In this world, the north settles California quickly and early. Realising the West is going to be controlled by Free Soilers the South puts all its focus on taking Mexico and Cuba.