Basic Chess Ending 7 - Two Bishops

 There is no box strategy for mating with the two bishop. Instead, there are following principles at work:

1. Use the Bishops to cut off two "connected" diagonals at the same time. This traps the defending King in one sector of the board.
2. The Bishops will be able to take away other important squares while also making whole diagonals impassable.
3. The player with the two Bishops must utilize his King more aggressively.
4. Chase the defending King to a corner.

In Diagram, the starting position is as poor as it could be for the superior side. White will have to drive Black King to the side and eventually to one of the four corners.

White to move

1.Bd2

White Bishops control the el-a5 and fl-a6 diagonals. Black King can't pass through this "fence"—a fence White intends to shrink when the time is right.

1...Ke4 2.Ke2 Kd4 3.Kf3

3...Ke5 4.Be3

3...Kd5 4.Kf4 Kd4 5.Be2 Kd5 6.Be3

4...Kf5 

4...Kd5 5.Kf4

5.Bd3+ Ke5

5.Bg2 Ke5 6.Kg4 is also good.

6.Be4 Ke6 7.Bf4

The diagonal Box has shrunk. Now White controls hl-a8 and h2-b8.

7...Kf6 8.Kg4 Ke6 9.Kg5

9...Ke7 10.Kg6

9...Kd7 10.Kf6 

10...Kd7 11.Kf6

10...Ke6 11.Bf3 (Waiting move) 11...Ke7 12.Bg4 Once again shrinking the Box by laying claim to the h3-c8 diagonal.

11...Kd8 12.Ke6  Depriving black King of the d7-square.

11...Kc8 12.Ke6 Kd8 13.Bb7

12...Ke8 13.Bc7

The final phase: White takes away the d8-square and herds black's King towards the h8-corner.

12...Kc8 13.Bf3 (Waiting move) 13...Kd8 14.Bb7 Ke8 15.Bc7

13...Kf8 14.Kf6

14...Kg8

14...Ke8 15.Bc6+ Kf8 16.Bd6+ Kg8

15.Bd6 There goes the f8-square! 15...Kh8 16.Kg6 (16.Kf7?? stalemate would be disaster)

15.Bc6? Kh7 16.Bf4 Kg8 17.Be4 Kf8 18.Bg6 Kg8 19.Bd6 Kh8 20.Be4 Kg8 21.Kg6 Kh8 22.Bf5 Kg8 23.Be6+ Kh8 24.Be5#

16...Kg8 17.Bd5+ Kh8 18.Be5#

Check my post on how to checkmate with two knights here.