The leading group trying to reform China into a nation-state was the Guomindang, but after 1920, the Chinese Communist Party was also in the mix. And for the Guomindang to regain power from those big landlords and reunify China, they needed some help from the CCP. Now, if an alliance between communists and nationalists seems like a match made in hell, well, yes, it was. That said, the two did manage to patch things up for a while in the early 1920s, you know, for the sake of the kids. But then Sun Yat-sen died in 1925, and the alliance fell apart in 1927 when Guomindang leader Chiang Kai-shek got mad at the communists for trying to foment socialist revolution, to which the communists were like, but that's what we do, man, we're communists. Anyway, this turned out to be a bad breakup for a bunch of reasons, but mainly because it started a civil war between the communists and the nationalists. We're not going to get into exhausting detail about the civil war, but spoiler alert, the communists won.