[Jacek]

The short story of the beginning of Barbarossa: Hitler cannot advance on Britain, therefore he decides to conquer USSR easily and
1) Get the Lebensraum he wanted for so long
2) Get hold of Soviet oil and other raw materials

However: some historians, more or less professional say: NO! The real reason was Hitler fear of a stab in the back. After USSR´s annexion of Bessarabia and N.Bukovina Stalin was just a few steps from the only oil fields Hitler could count on: Romanian. Morover: the bulk of Soviet army (RKKA) was ammassed at German border, ready for attack. German aerial recon has shown this on innumerable occasions. The annexiation of N. Bukovina was a flagrant provocation, against the terms of the Soviet-German pact.
RKKA transferred parts of its Dniepr Flotilla to the delta of Danube, thus forming a new Danube Flotilla, with lots of ships, amongst them - heavily armed monitors. The flotilla was theoretically able to help in the invasion of Romania and capture of oilfields - a lifeblood of Wehrmacht and all German economy.

Does history need rewriting?