Well lets see, here is a cursory look of American imperialism over the years. Its literally not possible to includ everything as there is simply so fucking much of it.
America's first overseas intervention was to protect trade routes and profits in the Mediterranean, against the Barbary pirates.
The US successfully ethnically cleansed and genocided 100's of Native American cultures.
At the end of the 19th century America annexed hawaii to gain control of its sugar plantations and production. It then crushed pro-democracy movements in Cuba, Puerto Rico and the Philipines and annexed those countries from spain.
Between 1900 and 1945 the United states overthrew the government of Haiti, reintroduced forced labor, banned haitian creole, occupied Honduras, annexed panama from Colombia to secure control over thr future panama canal
Between 1918 and 1939 the United States backed anti-communist as well as anti-democratic governments in Europe. American interests aided in the creation of Yugoslavia, Hungary an Czechoslovakia. Only Czechoslovakia became a democracy, though it was dominated by old Hapsburg era industrialists and landlords. The US backed the right-wing of the Chinese revolution during this time, after aiding in the suppression of anti-colonial revolts there in the 1890s and 1900s. America similarly sent tens of thousands of troops to crush the USSR in its infancy, part of a set of invasions that exacerbated and deepened the bolsheviks sense of siege. The US also supported british and french efforts to partition the former ottoman empire.
After 1945 the United States intervened in Greece to crush the communist resistance there, which led to fascist collaborators and old monarchists and nationalists seizing power there, creating the deeply unequal greece that exists today.
Between 1945 and 1950 American cash and cannon played a key role in securing european colonial posessions and restoring French control of Vietnam, which had won its independence at the end of World War 2. For the next twenty five years America bombers, soldiers and ships killed three million vietnamese, over a million Laotians and ultimately helped to entrench Pol Pot's regime in Cambodia against its more moderate challengers. This was explicitly for profit, as Vietnam was a major exporter of rubber and bauxite (Aluminum ore). After that Americans overthrew democratically elected governments in Syria, Iraq, Egypt and attempted to destroy Algeria.
In 1954 Jacobo Arbenz, the popularly elected president of guatemala was overthrown by after trying to put his country's infrastructure under the control of guatemalan government. He also wanted to introduce labor laws and break up the big banana plantations owned by United Fruit, an American company, which had him overthrown and replaced with a series of generals who killed 200,000-250,000 civilians in a Civil War/Genocide that lasted thirty years. This is the origin of the phrase banana republic.
In 1953 Mohammed Mossadegh, democratically elected prime minister of Iran, was overthrown by American backed generals after trying to transfer control of that country's oil fields to the Iranian people. The company which agitated for his destruction would one day become BP. The Shah then granted Anglo-American interests control of Iran's oil economy, while he suppressed all progressive and secular forces within the country.
In 1954-1963 the US ignored the referendum on Vietnamese unification and installed an anti-buddhist pro-french regime in a majority buddhist country.
In 1960 the United States overthrew Patrice Lumumba, democratically elected PM of the DRC, because he wanted to fully decolonize the country and investfully in food-independence and proper development. The Congo has been ruled by dictators or wracked by Civil War since then.
The 1975 Australian constitutional crisis, also known simply as the Dismissal, where the US intervened to have the PM of Australia replaced by a liberal one that would maintain cheap coal prices for the US at the expense of Australia.
In the 1960's and 70's and 80's the United States intervened and overthrew so many revolutionary, reformist or popular democratic governments that I actually can't list them all here, so here are the highlights: Inodnesia: the CIA fed Suharto intelligence that he used to massacre a million communists, socialists, union organizers and civilians in Indonesia. The US later backed the indonesian genocide in East Timor, which killed 300,000 people.
Mozambique: the Americans propped up the colonial government and its partisans against african revolutionaries in a war that killed a million people.
Angola: the US backed the colonial government, and then funded a reactionary, ant-labor, pro-resource extraction movement against autonomist and socialist forces in a war that killed two million people.
Chile: after revoking mining concession granted at the point of british cannon in the 19th century, Salvador Allende, the popularly elected and pro-indigenous president, was subjected to economic blockade, particularly of food-stuff that caused triple digit inflation. When this didn't topple him, the US backed Pinochet in a coup. Pinochet impoverished the average chilean, drove the country hopelessly in debt, tortured tens of thousands of dissidents, dropped trade-union leaders from helicopters into the sea, and destroyed indigenous rights movements.
El Salvador, Honduras and Nicaragua: in the 70's and 80's the United States fought a dirty war against democratically elected and popular revolutionary governments in these three countries, over control of infrastructure and whether they would be stuck as extractive cash-crop economies. These wars killed hundreds of thousands of people, destroyed Nicaragua in its entirety, and involved the famed Iran-Contra scandal, which saw Arms-for-hostages deals brokered to fund right-wing death squads, mass rape and war crimes against nuns. During this period the CIA used cocaine smuggling to fund the dirty wars, playing a huge role in the origins of the crack crisis.
Burkina Faso: In 1983 French and American troops and spies overthrew the president of Burkina Faso, Thomas Sankara, who had achieved food independence and vaccinated 2.5 million people in three years, while also combating female genital mutilation, illiteracy and rural poverty. Sankara was a communist, and true to his values his only possession were his books, his clothing, and his bicycle. He died, and with him died the dream of pan-african liberation and independence from the debt cycle.
In addition to these countries the United States has installed unelected governments, destroyed democracies in, illegally invade, or forced extractive trade relations on the following countries (all since 1945): Colombia, Brazil, Argentina (twice), Bolivia, Venezuela, Grenada, Sudan, Somalia, Cuba, South Yemen, Afghanistan, Iraq, Libya, Lebanon, the Czech Republic, most of the former USSR (particularly Russia, where the US stole the 1996 election for Boris Yeltsin, against Gennady Zyuganov), Haiti (thrice), Yugoslavia (American money was the key in Milosevic's rise and the fragmenting of Yugoslavia), the Philipines, and others which I have forgotten.
Between 1968 and the present the US has played a role in violently suppressing pro-democratic or anti-capitalist protest movements in: Saudi Arabia, France, Italy, The United States, Canada, Portugal, Germany, Yemen, Bahrain, Qatar, Morocco, Palestine, South Africa, Mexico and Thailand.
That's imperialism. The United States has never actually cared about democracy. When democracy was good for US profits, they backed democracy, when it threatened American profits they backed gangsters, landlords and fascists who smashed the hope of hundreds of millions. American imperialism operates by forcing trade concessions, low wages, bad working conditions and mal-development (infrastructure suitable only for extractive production) on the third world, most of the post-Soviet world, and even som first world countries.