Invasion of the United States

Throughout Resistance 2 and Resistance: The Gathering Storm, Nathan Hale (the main protagonist of the Resistance series) and the military forces of SRPA fought against the Chimera in an attempt to halt their invasion of the United States of America.

Pre-Invasion
Since before and after the Chimeran invasion of Europe and Asia, America had remained strictly isolated from world affairs under the Noah Grace Administration, and served only to protect its own agendas and interests. However, prior to Grace's presidency the American government and military had been aware of the Chimeran threat within Russia and was directly involve in foreign affairs in strengthening humanity's stance against the Chimera.

Finally realizing just how much of a threat the invaders were, the United States entered the war against the Chimera in July 1951 (only after the British had offered an exchange of a captured Chimeran Angel, however), and later successfully liberated Britain from the Chimera's control.

Beginning of an Invasion
Three months after the Liberation of Britain, the Chimera finally began to focus their attention on Earth's western hemisphere (for reasons ascertaining to their unknown intentions involving the Chimeran Towers). They began this Invasion of America by launching a Spire attack on the state of New York in August 14th, 1951. After New York was contained, the Grace Administration responded by creating the Liberty Defense Perimeter, a heavily defended safe zone in the middle of America.

Near the end of 1951, America's Northwest had been completely overrun by the Chimera (which officially made SRPA coined the term "Gray Territory"). The replacements of the Crawlers in place for Spinners greatly helped the Chimera in this conquest, as they could effectively infect populated cities within days (such is what happened to Chicago, Illinois). The Northwest invasion was only halted and impeded by the valor of the US Military, commando and Sentinel efforts in derailing the alien advance.

By this time, President Noah Grace had begun to rethink that the Chimera would inevitably take over the U.S. if they stayed at the rate they were going, and he secretly revealed (to the approval of most of his Cabinet) and executed a negotiation attempt with the leading Chimeran entity known as Daedalus, who was formerly known as Jordan Adam Shepherd, to spare America in exchange for the rest of the world; this plan was known as Project Omega. However, the negotiations failed as SRPA Lieutenant Nathan Hale killed Grace for his treachery to the human race. During this time, the Chimera had managed to take control of the nation's capital, Washington, D.C. (and, for that matter, nearly the entire East Coast), which forced the US government to relocate to Denver, Colorado that is within the LDP. The Chimera had also been neutralizing American interests in Alaska, most notably their assault of Fort Anchorage in January 1951.

The Chimera Gain Ground
Throughout 1952, the Chimera constructed and extensively used giant airships to bombard the American coastlines with spire missiles. The American Southeast was entirely blanketed with Spire attacks and was declared a gray territory, while on the West Coast the attempted invasion of Orick, California was contained by the forces of Specter Team. This change in tactics was due to the new leadership of Daedalus, who augmented with his military strategy among the Chimeran military caste and as well improving the chain of leadership with the introduction of Overseers and Primarchs.

Fearing the inevitable entire occupation of America and faced with gigantic amounts of human genocide by the Chimera, Grace's successor Harvey McCullen drafted a colonization plan of the Hawaiian islands, dubbed by the news press as "Operation Aloha". However, the operation later became an apparent failure when the entire islands' colonist population (including military personnel) mysteriously disappeared without signs of any conflict.

The Beginning of the End
On May 1953, Daedalus ordered his airship fleet to massively invade America's West Coast which, if taken, would allow the Chimera to surround the US military on all sides.

By May 28th, the Chimera finally breached the Liberty Defense Perimeter at the southern border and caused the loss of estimated to be 63 million human casualties. Among those that have died was President McCullen and his cabinet. All remaining human survivors totaling about 7 million scattered over America, and which only 2 million were relocated by American military forces to Baton Rouge, Louisiana, the last remaining protection camp in the nation. General of the Army Douglas MacArthur became temporary leader of the civilian population until orderly elections could be held.

Operation Black Eden
Despite the nation crippled by the invasion, SRPA made a last desperate assault on stopping the Chimera's intentions over the Chicxulub Crater by initiating Operation Black Eden in late June. The operation involved in placing a fission bomb within Daedalus' flagship and detonating it, destroying the remainders of the Chimeran fleet and Daedalus' plans. The operation was a success, as the fleet was annihilated in the nuclear explosion and Daedalus was killed at the hands of Nathan Hale. However, the success was only partial in that many soldiers (including Nathan Hale) died, and Daedalus' leadership system of Primarchs and Overseers still stood. Furthermore, Daedalus' mysterious plans apparently succeeded with the apparent teleportation of Earth to another part of space.

Note
The name of the entire invasion is never officially called as the "Invasion of the United States" and is used only in naming conjecture for a unnamed and recognizable conflict.