Chess Opening Theory/1. e4/1...e6/2. d4/2...d5/3. e5/3...c5/4. c3/4...Nc6/5. Nf3/5...Qb6/6. a3

=French Defence: Advance Variation= By playing 6.a3 White eliminates any possibility of a b4 intrusion. Also White is preparing to assert himself on the queenside via b2-b4.Furthermore, b2-b4 frees the c1 bishop from minding the b2 pawn.

Theory table
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1.e4 e6 2.d4 d5 3.e5 c5 4.c3 Nc6 5.Nf3 Qb6 6.a3