The Dutch Defense (1.d4 f5) is one of the most uncompromising defenses to 1.d4. A lot of people are afraid to play it because White has a lot of sharp ways to try to destroy it, such as the Staunton Gambit (2.e4), 2.Bg5, and 2.Nc3. Illinois master Alan Watson wrote a book in 1995 about various anti-Dutch gambits with g4, including 2.g4, 2.Qd3 d5 3.g4, and 2.h3 followed by 3.g4. If Black knows the theory, or can manage to find the right moves over the board, he or she can successfully counter all of White's sharp lines. If not, Black may be in for a nasty shock, as in the game below.
Take a look at the diagram position. White has sacrificed a pawn to obtain semi-open g and h files - sort of like a kingside Benko Gambit. At first glance, Black's last move, 5...Ng4-f6, might seem like a reasonable move, holding onto the extra pawn. At second blush, you realize that it is a terrible blunder, which is simply annihilated by White's sixth move, which mates or wins a rook.
Korchnoi introduced 2.h3!? and 3.g4 to modern master play in 1979, winning a crushing victory against the Swiss master Kaenel. The point is to avoid allowing Black to return the gambit pawn with a timely ...g3, e.g. 1.d4 f5 2.Qd3 d5 3.g4 hxg4 4.h3 g3 ("!" - Watson) 5.fxg3 Nf6 6.Bf4 c5 7.c3 Qb6 and Black stood well in Quigley-DeFotis, Midwest Masters 1985. It wasn't long before analysts found the strongest defense to Korchnoi's 2.h3. Well, actually rediscovered it - well over a century earlier Howard Staunton (yes, he of Staunton Gambit and Morphy-avoiding fame) had recommended declining White's gambit with 2...Nf6 3.g4 d5! 4.g5 Ne4, leading to an even game (The Chess Player's Handbook (1857!), pp. 381-82). One hundred and thirty-two years later, GM Larry Christiansen and IM Jeremy Silman recommended the same line (Dutch Defense (1989), p. 144), referring to 3...d5! as "Christiansen's move." Nothing new under the sun and all that.