Roosevelt Corollary was born out of the Monroe Doctrine. The Doctrine was the USA's foreign policy towards Latin America and European involvement therein. It was a surprising move when it was announced, since the USA was yet to rise to the position of the sole global superpower that it now enjoys. The Monroe Doctrine stated that though the USA wouldn't interfere with existing European colonies or the internal working of the European countries themselves, they would police any further intrusion by European countries in the Western Hemisphere.
Did You Know?The Roosevelt Corollary was based on President Theodore Roosevelt's famous 'Big Stick' ideology. The ideology centered around peaceful negotiations while simultaneously threatening the other party with military strength. 'Gunboat diplomacy' is also a fairly accurate representation of Roosevelt's policy, since his plans were based largely on the USA's naval strength.
The Roosevelt Corollary was formulated out of Roosevelt's imperialistic ambitions. The summary of the Corollary was that in accordance with their role as the preeminent power in the Western Hemisphere, the USA would interfere in any conflict within a Latin American country, to establish order and keep the country safe from potential European invasion.
While the stated intentions behind the Monroe Doctrine were honorable, the Roosevelt Corollary was used as justification for American interventionism in Latin America.
At the time the Monroe Doctrine was established, in 1823, European powers were being forced out of the Americas. Mexican War of Independence against their Spanish rulers was close to fruition, though it would take a bit longer for it to be officially recognized, Brazil would gain independence from Portugal in 1825, Venezuela had formed a republic in 1811, Colombia was free by 1819, and Argentina had gained independence from Spain in 1816. This contemporaneous rise of nationalist movements across Latin America was backed in the Monroe Doctrine.
However, in the first half of the 19th century, the USA was simply too weak to enforce its stated intentions. As a result, European powers didn't pay much attention to it, though European imperialism in South America carried on with the slow exit it was already suffering.
By the time Theodore Roosevelt, Jr., came to power, the USA had shed off its old image, and was emerging as a new global power. It could take a much tougher stance, and could actually follow through with its plans if need be.
Roosevelt's expansionist ideology received a willing ally in the Monroe Doctrine. He formed the corollary that if any Latin American country suffered from internal unrest or a downturn in economy―conditions that would provide European powers a trapdoor to enter the political scenario of the region―the USA would interfere militarily to reestablish order. The USA's superior navy gave Roosevelt the power to carry out his stated intentions. To sum it up, Roosevelt flipped the Monroe Doctrine on its head, barring European powers while simultaneously doing what the Doctrine didn't allow the Europeans to do.
Consequently, Latin America started to harbor animosity towards their northern neighbor. The Platt Amendment with Cuba turned the Caribbean country into little more than a protectorate of the USA. From 1906 to 1909, the U.S. even ruled Cuba. Roosevelt also instigated and aided the nationalist movement in Panama, which was a part of Gran Colombia at the time, in order to facilitate his pet project, the Panama Canal. Over the first 30 years of the 20th century, the USA invaded Cuba, northern Mexico, Nicaragua (twice), Dominican Republic, Gran Colombia, and Chile.
The Roosevelt Corollary was gradually phased out of American foreign relations under the administrations of Calvin Coolidge, Herbert Hoover, and Franklin D. Roosevelt, who adopted successively more tolerant and less interventionist policies towards Latin America. FDR's 'good neighbor' policy was the final nail in the coffin for Roosevelt's expansionism. The latter Roosevelt's policy stressed non-intervention and non-interference in Latin America, and promoted two-way economic ties with several countries.