I imagine, sclerotic political will has turned over the US advantage to China by 2035. The Chinese, learning absolutely nothing, will continue to grow ever more corrupt, as they slowly join the United States in Stagnation, and repression. Failure to compromise has led to multiple outreaks of Violence amongst americans, including possible fascisim, until the united states is warped into a repressive state simply to turn back the tide of sectarian ideological violence. As liberties are slowly constricted, random acts of violence grow less-frequent, and the united states has returned by this period to relative stability. The march of technology has allowed the government unprecedented control of it's citizenry, and only a few bastions guarenteed by international law remain.
Moreover, living conditions have suffered. The long period of political (and all in name actual) warring between the partisan factions has left the united states a stagnated hellhole, where crumbling infrastructure is far inadrquate to sustain the needs of the populace. Global warmoing continues, slowed, by steady, and the united states is by all means still a world-power due to having large control of remaining resources, including water and arable land. Industrilaization of Agriculture occured to fight back the ongrowing tide, and many new jobs are in that sector.
By this time, Brazil has emerged as a Significant Power in the world, and the middle east has receded as alternative sources of power become dominant, including untapped resources long-unexploited. Iran is a nuclear power, but one on par with modern Pakistan and North Korea, a failed state held together by threat of annhilation. Japan grew more and more along the lines of the united states, and following the War of the South China Seas, where Japan fully re-established itself as a military power, with US aid, it has become similar culturally to the modern US, a fraught alliance of left and right leaning interests held together by the common good. India grew larger, and more powerful, but its growth was not enough to bind together the poorer areas, and India split. Europe remained stagnant, economically, militarily, and culturally, until 2030, where it eventually grew to be a homogenous government. However, Britain, and several Independatist factions, have pushed back, eventually forming a alliance of European nations hostile to the New EU. For now, The Continent, and the Opposing Faction, composed of Neutralists, the eastern nations, and led by Britain oppose the EU for dominance.
The City of New york did what it could, and Acted aggresively towards it's neighbors. eventually aligning with the State Government. The Resource Rich, Economically rich state was able to bully the Nearby states, continually getting better and better Deals from them, until It became the Sole Powerholder in the region. During the period of weak central government, the State was in its highlight, bullying the National government and other nations alike for materials. Following the Reconstitution of the US Government, many of the NY Politicans were jailed, for various fradualant reasons, to break resistance in the area by the men accustomed to power.
The United States entered a Isolationist Phase following the Horrors of War, Breaking once only to Join the Japanese in the South China Sea. This continues until the late 2040s, where demands for more resources and competition from in northen neighbor forced the US into invading Canada. The small Canadian Population put up quie a resistance, and the region was mostly uncontrolled until the mid 2050s, when the US government underwent its Centralization, during which the famous "taming the wilds" campaigns were fought. Many Innocent Candians were slaughtered, a fact covered up by the US to this day.