Europe is the primary battleground in the history before Resistance: Fall of Man and the battleground during Resistance: Retribution. Many countries in Europe were part of the United European Defence and the European Trade Organization. Despite these united countries, the Chimera broke through Europe's border with Russia, overrunning the continental Europe in just three weeks, and Britain in three months.
Following the end of the Great War, when Germany declared a ceasefire and was reestablished as a parliamentary democracy under the Weimar Republic and the signing of the Treaty of Versailles in June 1919, the European Trade Organization (ETO) was formed with the purpose to encourage all European nations to cooperate to establish peace, thus avoiding future devastating conflicts similar to the Great War. In the following decades, the ETO accepted new membership from European countries. The organization also helped to restore war-torn Germany into becoming an ETO member, allowing the Weimar Republic to triumph over the National Socialist Party. This in turn stabilized the continent, and allowed further economic developement and progress. However, Russia, having been a member of the Allies during the Great War, didn't join the ETO on the belief that Europe and its organization was anti-imperialistic and posed a threat to the Russian autocracy ruled by Tsar Mikhail. This belief also led Russian government authorities to capture and execute tweleve French agents without trial for supposedly encouraging insurrection within Russia. And for these reasons, Russia isolated itself from the world by closing out all outside communications and constructing a barrier along the Russian/European border known as the Red Curtain. As a result, a tense cold war was developed between Western Europe and Russia.
Despite Russia's isolation, Europe enjoyed lasting peace through the 1920's and 30's, with Germany hosting the Olympic Games in August 1936, where American athlete Jesse Owens became the first American to win four gold medals in a single Olympics. However, sudden unexplainable occurrences had been coming from Russia, such as unnaturally cold weather that caused 138 people and many animals to freeze to death in Sweden; a mysterious slick containing exaggerating quantities of radon coming from Russia's Volga River that flowed into the Sea of Azov, causing the deaths of all the sea's marine life and several villagers; and the appearance of Russian ghost towns appearing across the Belorussian border that showed no signs of violence, which led European intelligence to believe that chemical and biological weapons had been involved. With the latter information, the ETO became greatly concerned of Russia, and through its security branch, the United European Defence (UED), created the Military Defense Commission (MDC) in May 1939 in Luxembourg to focus on weapons research and development. Between the 1920's and 1940's, the relationship between Europe and the United States of America was fairly cooperative in its cross Atlantic trade, despite it being strongly opposed by American isolationist elements, such as Senator Robert Taft. However, in November 1940, following the American presidential election of Noah Grace, he firmly reestablished America's isolationism and cut off "political and military endeavors" with Europe.
By the 1940's, Europe further reported mysterious accounts of strange unidentified flying objects in eastern Europe; an unknown Russian refugee that appeared in a British embassy in Estonia carrying a strange skull; and Russian cities suddenly being abandoned. Becoming even more concerned, European intelligence agencies tried to listen in to Russian radio broadcasts, only to hear a single message repeated over and over again in Russian across a network of 12,000 stations with the words "Brotherhood, strength and fortitude... in the face of the angry night." Two days later a British MI6 listening station in the Ukraine intercepted electromagnetic radiation emanating from Russia. The powerful signal caused the receivers to overheat and electrocute five men. It was sometime that European intelligence learned about the existence of the Chimera.
In April 1949, King Edward VIII of the United Kingdom visited the United States and privately talked with President Grace in regarding to the Chimera, and encouraging his nation to support Britain and Europe whatever it can. Meanwhile, further strange occurrences were leaking out of Russia, including incidents of freakish snow storms and a stampede of mixed animals in the Ukraine. In December 1949, the Chimera breached the Red Curtain and invaded Europe, leading to millions of people being either killed or infected within three months time (December 1949-February 1950), with Britain being the last European nation to be free, only to be conquered later on in October 1950.
It was not until the liberation of Britain that the European continent was likewise freed from Chimeran control during Operation Overstrike, as joint British and Maquis forces succeeded in destroying the hub tower in Paris, France, causing the en mass deaths of nearly all Chimeran forces in Western Europe. By 1952, European allied forces had been fighting on multiple fronts in Europe and were planning an assault into Russia.