Warning this time line is FICTIONAL and in no way related to reality. This may seem anti-American but there is no offence intended this is for entertainment purposes ONLY.
Between the years 1920 and 1930 the united states created the color-coded war plans. These plans where meant for war to control the world. However these plans where never used except for 1. war plan orange was used in World War II as a template for an invasion against the Japanese empire. The rest of the plans where scraped and archived. But what if the plans where used? The following is a time line of what could have happened.
Nazi- Germany Empire- British Imperial- Japanese Soviet- Russia
1921: USA invades Mexico and dominance is established in 1923. All trde with Mixico was cut off and tentions between USA and Mexico Allies.
1922: USA invades the Portuguese Azores islands. Only a month in USA dominance is established.
1922: USA invades Cuba, Philippines and Latin America full control is established in 1929.
1929: British empire orders for martial law in the empire. Canadian borders become heavily defended.
1933: Adolph Hitler becomes leader of Germany but gets nervous due to the USA occupation of Latin America.
1934: The USA invades Canada heavy casualty's on both sides. USA controls Canada in a matter of months.
1935: USA invades imperial Japan but is hampered by royal navy ships. Southern Japan is occupied in 1936. Japanese royal family is extracted to London by royal navy ships.
1935: A conference is called by the British empire. And invites Hitler, emperor Showa and leaders from other European nations. To decide what to do about the USA. During this time American forces in Canada are dealing with rebels.
1935: USA uses southern Japan as a staging area to invade China. Eastern China, Mongolia and Hong Kong annexed in 1938 empire trade routes disrupted. China fully annexed in 1942.
1936: Europe, British empire and the Japanese empire decide to fight against the USA. World war II declared.
1936: Soviet Russia declares neutrality in the war.
1937: Germany starts mass production of vehicles and weapons along with France and the Empire. The Japanese monarchy is offered asylum in London but kindly refuse and move to Australia to help the Empire invade southern Japan.
1938: American forces in Japan are hampered with resistance forces and militia.
1938: American forces invade middle east but are hampered by French and Nazi forces with help from the RAF.
1938: Empire forces in India move into China with help from Imperial forces in Korea.
1939: Nazi forces move into Afghanistan to prevent the nation to be used as a staging area. British SAS created for disable American air forces and 'special operations'.
1939: US naval ships are destroyed by royal navy and Imperial naval forces. Pacific blockaded.
1939: USA invades Russia despite neutrality agreements. Soviet forces have trouble keeping American forces at bay.
1940: Nazi, Empire, Europe and imperial forces issue light body armour to troops for extra protection.
1940: Japanese scientists create the worlds first mech. Blueprints are given to their allies. Each nation creates their own mech.
1940: Germany issues the world's first assault rifle. Empire, Imperial and European forces then create their own assault rifle.
1941: Reports of people being forced into the American army start to suffice.
1941: American forces in China suffer from raids by rebels but still hold China.
1942: US forces in middle east are pushed back into China.
1943: Western China secured by Nazi and Empire forces. Southern Japan is liberated a few months later. American forces in China and Russia are cornered but still fight.
1943: US starts construction of coastal defence guns on the eastern and western seaboard. They also start the construction of anti-air mechs.
1944: With dwindling supply's the American forces in China and Russia surrender to Nazi and Empire forces. China slowly recovers and offers food, water and shelter to Nazi and Empire troops.
1944: The soviets send the Americans to China where they become prisoners of war. At this time Empire, Nazi, Europe and Imperial army's get ready to liberate Latin America.
1945: Operation Latin star begins as 100,000 Empire, Nazi, Europe and Imperial troops along with 5,000 tanks and 4,000 mechs are deployed into Chile and Argentina. Southern Latin America liberated in 1947.
1945: Empire forces deploy 7'000 paratroops, 400 tanks and 300 mechs into Canada. American forces leave Canada after 7 months of fighting.
1947: Coastal defence guns are completed.
1948: Empire, Nazi, Imperial and European forces attack northern Latin America. The northern part of the continent is secured in 1950.
1950: 3 highly classified objects are brought to the pacific fleet.
1950: the city's of Springfield, Pittsburgh and Pennsylvania are destroyed by an explosion of unimaginable size. The American president then signs a declaration of peace.
Post war time line.
1952: British colony's start an uprising causing the empire to fall. Britain then establishes the commonwealth nations.
1952: Adolph Hitler dies of an unexplained disease. With no successor Germany goes through a power struggle. But the Nazis never won the elections again and fell apart and died.
1953: China fully recovers from the occupation and starts reconstruction of city's. And reluctantly accepts financial help from Japan.
1953: The British SAS became a special forces group. They rapidly become the beast special forces group in the world.
1954: After the occupation of central Russia tensions grew thin as an internal power struggle began. This ended the USSR and the soviet regime as the Russian federation is born.
1955: Due to the accomplishment of the mech scientists worked on ways to incorporate it into civilian life. The 'worker mechs' where a successes and are accepted all over the globe.
The rest of it you can find in the history books. In this fictional universe there was no cold war, no Vietnam war only terrorist attacks. You can use you imagination for the rest.