The origins of the Cold War can be traced further back than 1945, up to post-World War 1. In the period 1918-1939 interwar diplomacy between the Soviets and West did not amount to any mutual co-operation between them.
The Russian Revolution of 1917 brought to a close the Russian involvement in the 'Great War.' The Treaty of Brest-Litovsk saw a lot of Russia's western territory in Eastern Europe stripped from them by Germany. Russia had little choice but to agree as they could not continue the war, while the West denounced the terms drawn up by Germany.
However, the Bolsheviks were able to consolidate their regime in Russia and the treaty had brought peace in the East. As such, the treaty was of some value to them.
Versailles was the most dominant treaty signed in the period to bring World War One to a close and usher in a hoped for new era of world peace. Alas, this treaty was primarily a treaty drawn up by the Entente; and did not include any Russian input. Russia, grateful that Brest-Litovsk had been overturned, weren't so pleased with an independent Polish state that had been under Russia hegemony for a generation. However, it was far better for them than Brest-Litovsk; and Germany was also demilitarized.
The West did not recognize the Soviet regime, which preached world revolution through Communist International. The Russian Civil War of 1918 included Western troops who sought to defeat the Bolsheviks in Russia as well as regain lost munitions. Alas, it was to no avail as the Bolsheviks consolidated. This Western military involvement was, however, an early origin of the Cold War.
An interesting piece of diplomacy between Germany and the Soviets was the Rapallo Pact in 1922. Then the USSR came to better terms with Germany to co-operate in a spirit of mutual goodwill in meeting the economic needs of both countries. To this end, the USSR allowed for Germany to undermine the Treaty of Versailles by training their military in the USSR. It was a settlement that further undermined Western-Soviet relations.
The West countered this with the Locarno Pact, which also courted Germany. Germany entered the League of Nations and made defense provisions with the West. The USSR was not at the bargaining table and saw it as a Western détente.
Despite the Bolshevik victory in the Civil War, and their New Economic Policy, things did not improve. Lenin passed away, with no clear successor nominated. The rise of Stalin followed.
In 1933, Germany elected the Nazis and Roosevelt became U.S. president. With that the USA finally recognized the USSR, and the Bolshevik government in that same year. This was an improvement in relations with the West, but it was not enough in its self.
Britain and France were still a little uneasy, and with the USA isolationist they signed the Munich Agreement with Germany in 1936. The Soviets were not invited to the conference either, and it was hoped the negotiations would ensure peace in Europe.
As such, the USSR became closer to Germany and signed the Nazi-Soviet Pact in 1939. Certainly, this was a defensive alliance, and allowed for German military occupation of Poland. Britain and France declared war with Germany. However, the Soviet agreement with Germany was also noted by the West.
The period 1918-1939 saw a lot of diplomatic maneuvers between the West and the USSR, largely involving Germany. This resulted in an uneasy military alliance with the USSR, born out of conflict - but nothing else - in 1941. During the interwar period, the West had not found any diplomatic agreement with the USSR. As such, the origins of the Cold War can be found in Rapallo, Locarno, Munich and the Nazi-Soviet Pact - along with the Western military involvement in the Civil War.