A Century of Chess: New York 1918
There are two great opening innovation stories that both come from 1918. One is the introduction of the Budapest Gambit — a group of minor Hungarian masters passing on the secrets of the Budapest at a tournament in Berlin, which led to the ambushing of Akiba Rubinstein, the leading 1.d4 player of the era. And then there’s maybe the most famous opening story in chess history — Frank Marshall’s hoarding of the Marshall Gambit for years, waiting to spring it on Capablanca, then finally doing so at New York 1918, achieving a powerful attack out of the opening, but with Capablanca somehow clawing his way to victory.
As with all opening stories, aspects of it don’t entirely hold together. Marshall and Capablanca were frequent opponents during the 1910s. In several games with the black pieces, Marshall opted for the Petroff. But what is indisputable is that the Marshall Gambit is one of the great opening ideas ever — like a judo move where black suddenly takes the initiative in the Ruy Lopez — and Capablanca, utterly ambushed, had to work out all its complexities over the board, which he did about as well as anybody could be expected to.
Capablanca’s win in that game set the tone for the rest of the tournament, which was just another pearl in his long string of successes, nine wins and no losses, part of his undefeated streak that would continue until 1924. The tournament is a testament to his defensive skills — not only in the Marshall game but withstanding a frenetic attack by David Janowski.
Most of Capablanca's wins, though, were his usual unruffled positional clinic.
The tournament is of a piece with a series of other events held in New York in the 1910s — all of them won by Capablanca without much challenge. But, by 1918, American chess had gotten impressive. Janowski and Kostić arrived in the middle of the war, and — in contrast to the cozy, parochial tournaments from a few years earlier — it would have been reasonable at this point to consider New York the epicenter of the chess world.
The tournament, together with Hastings 1919, was the career high point for the Serbian player Borislav Kostić. He finished second, playing in a stately, low-key style, although the result was a mixed blessing for him — leading to an overestimation of his abilities and to a really scarring match defeat against Capablanca in 1919.
The tournament is also a good moment to appreciate Oscar Chajes, who was one of the stars of the decade but just short of being a world-class player. Chajes had some great scalps over his career — most famously against Capablanca in 1916 but also winning the brilliancy prize here for his win over Janowski. He had a solid style and an eye for the shot but could also get badly outplayed.
Between the workouts of the Marshall Gambit and the Sicilian Dragon at this tournament, a fairly distinct American style had emerged — rough and ready, with a willingness to mix it up tactically, and with relatively less interest in the 'objective truth' of a position. 
Sources: Edward Winter, as one might expect of him, has an extraordinarily detailed article on the origins of the Marshall Gambit here. Capablanca annotates several of his games in Chess Fundamentals.
