Modern Attack, Bardeleben Variation

The Bardeleben Variation is Black's answer to Steinitz's 5. Qe2 in the Modern Attack of Petrov's Defense, also called the Russian Game. The knight leaves the e-file with 5...Nc5, and after White regains the pawn with 6. Nxd4, Black develops with 6...Nc6, hitting the centralized knight and targeting e5. Material is level. White keeps an advanced e5-pawn, while the queen on e2 temporarily obstructs the f1-bishop. Black's main alternative at move five is 5...Bb4+, considered sufficient to equalize.