Patton was a virulent anticommunist and saw the Red Army as a tool spreading communism into Europe. Patton, like a lot of conservatives at the time of World War II (J. Edgar Hoover is another example) was influenced by the Red Scare that took place following the October Revolution that gave birth to the Soviet Union. During this scare, which lasted into the 1920s, many Americans and Europeans believed other countries would follow the Soviet Union into revolution.

During the war, Patton's anticommunist beliefs were reinforced by his encounters with members of the Allied armies. From The Patton Papers, Volume 2 page 734:

"Lt. Gen. Bishop Gowlina of the Polish Army came to see me and stayed to lunch. He is a very bright man, speaks perfect English, and hates the Russians with reason. He told me some of their methods. ...

According to the Bishop, more than two million Poles have been taken to Russia for slave labor. In every case ... they split families ..."

Patton's beliefs were partially racist as well. Again, from The Patton Papers, Volume 2:

"The difficulty in understanding the Russian is that we do not take cognizance of the fact that he is not a European but an Asiatic and therefore thinks deviously. We can no more understand a Russian than a Chinaman or a Japanese and, from what I have seen of them, I have no particular desire to understand them except to ascertain how much lead or iron it takes to kill them. In addition to his other amiable characteristics, the Russian has no regard for human life and is an all-out son of a bitch, a barbarian, and a chronic drunk."

Those excerpts were from Patton's diaries, which are as direct a source of his internal thoughts as you're going to find. Almost immediately after Patton's death, War as I Knew It was released. This history used selected bits of Patton's diary and papers to give the vanilla version of his thoughts. The more caustic items are still becoming more widely known.

War as I Knew It is useful to illustrate some of the missed opportunities as well. Patton's attitudes could have changed had he been in actual contact with Soviet authorities, but again and again, he shied away from direct meetings: "Huebner told me that when and if I met any Russians, I must be prepared for mutual exchange of medals, flags, and personal equipment, and that for that reason I had better not wear my good pistol nor my expensive watch, as I would certainly not get the equivalent from the Russians in a swapping match."

One of Patton's biggest splashes was at the press conference of Sept. 22, 1945, at which Patton let his feelings about communism known, full blast. "My language was not particularly politic," he euphemistically wrote. "I am afraid that our foolish and utterly stupid policy in regard to Germany will certainly cause them to join the Russians and thereby insure a communistic state throughout Western Europe."