Is this the United States with today's borders? I hope not. But I'll write a scenario.
Because I think an Articles of Confederation POD is the best way to achieve this. Basically have the whole thing fail and escalate into more and more conflict between the states, eventually resulting in decades of civil wars, like in Argentina, punctuated by even more serious conflicts both internal and external (War of 1812, say). Some Western filibusters manage to grab Louisiana and New Orleans at this tim. Maybe by 1830 or so things get a bit more stable as General Andrew Jackson (with his prestige as the hero of New Orleans as in OTL) re-unites the states by the sword, and the following decade the United States conquers the Mexican North. After Jackson's death we get some more low-level civil war, followed by a new dictator imposing their will in Philadelphia (Washington DC?--we'd love to build a city like that, but we don't have the money!), sparking a major civil war lasting nine years, helped by the unusual amount of outside support. Since the South is the nucleus of this new rebellion, slavery gets abolished to punish the South and many plantation owners get the firing squad with their land given to their former slaves (though other plantation owners get to effectively re-enslave their slaves through with Black Codes and such). In the North, the capitalist system still takes off and oppressive labour conditions are the norm. The country tries to rebuild, but border incidents with Britain over the northern border cause intense tension in the 1880s. The United States fights a 5 year war with Britain over these border disputes, only ended by the deposition of the ruling president and the promise by Britain to not restore Mexican land, a very real threat.
All the while, the United States spends massive amounts of money on her military, and unlike OTL receives much less immigration, although some are still lured by the burgeoning industries on par with Brazil or Argentina or likewise the chance to own land. This also introduces the ideology of socialism to the United States. Labour suppression in the 1890s - 1920s is far, far worse than OTL. At the end of the 1920s, a global depression grips the world, and the United States fights yet another civil war, the Second American Revolution, a decade-long struggle between communists under their charismatic yet brutal leader Comrade Johnson and anti-communist forces that goes endlessly back and forth with huge amounts of violence on either side before finally the communists hoist their red banner over Independence Hall as the new United Socialist States of America. The communist regime is hit by one disaster after another, like the 1950s famine caused by the return of the Dust Bowl. Adopting pseudoscientific methods to fix the problem, it actually gets far worse and large swathes of the Great Plains remain almost permanently useless. The regime is practically synonymous for "environmental disaster" in many other areas. Domestically, with every new ruler the government embarks on purges of both the military and the societal elite--gulags containing millions of people exist in remote regions of the Rockies and Southwest. Huge amounts of income is wasted on military projects intended to defeat the regime's chief ideological rival, the Anglo-French Union, to not even speak of the massive amounts of support given to regimes and rebel movements throughout the planet. After another drought in the late 1980s, the USSA begins to collapse in on itself, leading to even more brutal reprisals. Hypernationalism is promoted even more as the new ideology. The son of Comrade Johnson, nicknamed "Comrade Jr." seizes power using his father's legacy as a legitimiser. Comrade Jr.'s rule is totalitarian, extreme, and brutal, even by the standards of the USSA. Civil war occurs throughout the 1990s, before the government finally suppresses it. Comrade Jr. dies in 2013, leaving his son, nickamed "Comrade the Third" in charge of the family dictatorship which detractors call the "Johnson Dynasty" but supporters viewing Johnsonism as the only force which can save the USSA.
Although research on nuclear technology was hindered for decades because of its "anti-socialist" nature and the defections of many scientists, under Comrade Jr. the government has rapidly acquired nuclear weapons and has begun a global arms race, pointing these nukes at every major city on the planet. While many Americans live in 2017 conditions little different than 1917, with rampant poverty and a country often on the brink of famine, the USSA possesses the world's largest military and nuclear arsenal, clearly making it a power to be feared.
Meanwhile in the Middle East, the only thing sunnier than the beaches is the economy...I'll leave that to someone else