Localism reasserted itself, with large-scale landlords, with small-scale armies ruling all the parts of China that weren't controlled by foreigners. You might remember this phenomenon from earlier in Chinese history, first during the Warring States period, and then again for 300 years between the end of the Han and the rise of the Shui. So the period in Chinese history between 1912 and 1949 is sometimes called the Chinese Republic, although that gives the government a bit too much credit. 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.