The US Postal service was created in 1970 to reduce illegal transportation of horse legs. At this point horse leg trafficking has been a problem for years but the situation became urgent in 1966 after a horse leg related mass murder. This drew attention to the danger of horse leg trafficking, making it a hot button issue. Richard Nixon pushed for harder enforcement of anti-trafficking laws but while in office he legalized, and started regulating the industry, greatly reducing the danger.
After it's controversial start the postal service has continued to be radical. In the 1980's they sacrificed 7 senators to the moon god, Kevin. Many believed the earth god, Mary needed those sacrifices. Some radicals thought the sun god, Ibarkonse needed more power. The conflict was solved by the US military killing 7 people per god per state but subtracting the 7 from Kevin's total.
In 1995 the postal service declared war on Europe. Europe was confused and scared. The fighting started in Italy with the postal service opening hell portals on the battlefield, making it obvious they were not here for prisoners. The fight for Italy took 3 days, an impressive feat to be sure. Next was France. At this point the postal service got board of this war and just nuked the capital of every European nation. Victory was theirs. The literal hell scape Europe was after the war was a perfect place for the postal service to set up shop, declare independence and their goal of destroying the world.