American unreadiness would shape Britain’s opening strategy

How prepared was the United States for a war with Britain in 1914 or 1915?

Poorly prepared. Its small regular army would need time to mobilise, while Britain could reinforce Canada through an imperial system protected by sea power.

The United States entered the scenario with a small regular army and little preparation for a major coalition war. Britain would still have to protect Canada and other exposed imperial positions, yet it would have time to move troops while American forces mobilized. The Central Powers could not readily send comparable reinforcements across an Atlantic controlled by the Royal Navy. This imbalance makes the opening campaign a contest between American proximity and British access to a wider imperial military system. It also limits how quickly an American declaration of war could produce decisive pressure outside North America.