411 REFERENCE · Wikibooks
Chess Opening Theory/1. d4/1...d5/2. c4/2...c6/3. Nf3/3...Nf6/4. Nc3/4...dxc4/5. a4/5...Bf5/6. e3/6...e6/7. Bxc4/7...Bb4/8. O-O/8...O-O/9. Qe2/9...Nbd7/10. e4
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Dutch variation D19 Dutch variation Euwe variation
10. e4
White has been building up to this move for a while. This central expansion hits Black's light-squared bishop with tempo. Black has two squares to retreat the bishop to.
/10...Bg6/ lets the bishop keep an eye on the e4-pawn, which must now either be pushed to e5 or protected by White's bishop.
/10...Bg4/ immediately pins White's knight on f3, making the e5 pawn-break possible and also allowing various tactics revolving around the d4-pawn unless defended again.
Theory table
10. ... Bg6 11. Bd3 Bh5 12. e5 Nd5 + 10. ... Bg4 +
References
See also