Well, another good candidate could be America, a powerful nation that exceeds or equals (or at least exceedED or equalED) the previous enemies in terms of military might, reach, and influence can also be used in a work as powerful villains. Many times, they could be portrayed as the Well-Intentioned Extremists or Knight Templar with Grey and Grey Morality varieties.
Due to the potential for edit wars, No Real Life Examples, Please!
- In the manga of Bokurano, America is portrayed to be nation that threatens Japan. Some characters even wonder if they would invade, using Zearth's battles as an excuse. Subverted as the Americans haven't done anything yet.
- Code Geass averts this with Britannia. The Americas are the "Homeland", but the series takes place in an Alternate History where the American Revolution failed. They stayed as American colonies until the British Isles fell, making them the new homeland.
- Ghost in the Shell: Stand Alone Complex. The American Empire is depicted as being imperialistic (invading Central and South American countries) and committing war crimes. In the original series, American Empire CIA officers try to manipulate Batou into killing a former Imperial naval officer to cover up U.S. war crimes. In the 2nd GIG it launches a nuclear missile at Dejima, which would have killed all of the refugees living there.
- Mobile Suit Gundam SEED gives us the Atlantic Federation, a fictional nation made up of about all the Americas, with the intent on exterminating the Coordinators.
- In We Stand on Guard, America is now an authoritarian state which has invaded and occupied Canada to seize its natural resources (especially clean water) in order to replace its own.
- Captain America: The Winter Soldier: While the first film had the Captain punching out German HYDRA soldiers, the sequel has him fighting his own home nation, with HYDRA having infiltrated the American government and intelligence agencies, and building itself up again from the ashes with American recruits.
- The Alternate History mockumentary C.S.A.: The Confederate States of America features a world where the Confederacy took over the whole of America, becoming an imperialistic pariah state where white supremacy and non-white slavery are cherished American institutions up there with baseball and apple pie. The kicker: it's ultimately portrayed as Not So Different from the actual United States.
- In the second Illuminatus! trilogy, Schrodinger's Cat, Robert Anton Wilson and Robert Shea introduce "Unistat", an alternative-universe and somewhat more malevolent version of the USA.
- In The Laundry Files, while the Laundry, the British occult spy agency is definitely morally ambiguous, the American equivalent, the Black Chamber, is consistently shown as evil in its methods and goals. However, The Commstock Office was pretty reasonable until the Black Chamber got them shutdown
- Played with in Nineteen Eighty-Four. The story is set in dystopian Britain, but Oceania is primarily an American-based superstate. The other two superstates (successors of Russia and China) are just as totalitarian and imperialistic, however.
- Magical Cannon Wars features the US, most specifically the Pentagon, to be behind the whole conflict.
- The Big Bad of Modern Warfare 2 turns out to be an American General Shepherd, who starts World War III out of patriotism and the desire to restore U.S. dominance over the world.
- Zig-Zagged in the fourth game of Time Crisis, where Americans are both the main protagonists and antagonists.
- The United States in Fallout seemed to be a friendly, patriotic utopia full of wholesome families and cheerful optimism. However, it gradually transformed into a corrupt, jingoistic, Orwellian police state who saw nothing wrong with imprisoning their own citizens and experimenting on them. Corrupt corporate executives were in power everywhere, safety regulations were pretty much nonexistent, radioactive food was approved for stores, and the nation gladly invaded Mexico and later annexed Canada just to seize their resources. As the situation dragged on, riots from angry Americans lead to the government even opening fire on their own people with military-grade weapons. With a nuclear war as a real threat, they approved the construction of 122 Vaults to shield the civilian population. However, this was just a cover story, since the vaults were actually designed to subject their residents to cruel and sadistic experiments to see how people in enclosed environments react. And even after the Great War, the scattered remnants of the government survived, seeking to regain their power by killing off all the wastelanders so they can repopulate.
- Implied in Way Of The Samurai 4. Finishing all of the sidequests in this game will trigger an invasion of foreigners, which you, a group of local vigilantes and the Yakuza will have to thwart. Said invasion is led by a stereotypical American dressed in a cowboy suit, with his flunkies being dressed in western military uniforms, so it can be assumed these invaders are Americans, but this is never explicitly said.
- The Alternate History story Decades of Darkness has the United States, owing to a disastrous loss in the War of 1812 that saw the British (by way of Canada) take over the Great Lakes and the New England states, New York, and New Jersey secede as the Republic of New England, coming under the domination of the planter aristocrats of the Deep South. As a result, the US becomes a white supremacist empire that not only maintains slavery well into the 20th century, but extends it to the Latin American peoples it conquers (save for a few collaborators who can pass for white) as its armies push its southern border ever further south.
- In the Sequel Series to Fear Loathing And Gumbo On The Campaign Trail Seventy Two, the United States becomes a truly awful place in the 1980's. Donald Rumsfeld is elected president despite losing the popular vote by a decisive margin, and resorts to blatant voter fraud to earn a second term. He goes hard to work turning the country into a police state, his anarcho-capitalist policies create serious economic disparity, interstate travel is restricted, the civilian internet is strangled in its crib, Hollywood is transformed into a far-right Propaganda Machine that vilifies historic figures like FDR, dissidents (such as George Carlin, Barry Goldwater, and Roger Ebert) are "disappeared", Liberty Battalions start burning books that are deemed Anti-American or Anti-Capitalist, environmentalist polices are revoked and climate change is encouraged, the AIDS virus is studied as a potential bioweapon, and all of America's allies (sans Apartheid South Africa) are alienated, especially after Rumsfeld supports terrorism in Northern Ireland to "punish" the United Kingdom for voting in a labor government. He even privately admits he plans to repeal the constitution, aside from the Second Amendment, and plans to make himself President for life. You can't really blame all the states who decide to secede.
- And believe it or not, it gets worse. The Christian Values Party takes control after Rumsfeld is deposed, transforming the country into a totalitarian theocracy called the Christian States of America. Under the reign of Douglas Coe, congress is obliterated with missiles, many of Washington D.C.'s monuments are demolished and replaced with states of their interpretation of Christ, and the CSA has zero qualms about using nuclear weapons on any and all resistance. By 1990, a second American civil war has begun.