The reasons for this different political environment is only hinted here and there in the story, but apparently the Point of divergence is that the Civil War started in the 1850s and resulted in a victory by the Confederacy. As a post-war consequence, the US loses all ground west of the Mississippi River as American-claimed western lands secede from the Union and create their own sovereign countries in the wake of the victorious South. With the dissolution of most of its territories and influence, the United States is reduced to a struggling collective of the Great Lake and Northeastern states surrounded by hostile and powerful neighboring countries.