During World War I, the Chinese Government, such as it was, sided with the Allies. In return, they were promised that the German concessions in Shandong Province would be handed back over to the Chinese Government at the end of the war. They weren't, and to add insult to injury, the Treaty of Versailles handed them over to Japan. On May 4, 1919, about 3,000 students from various Beijing universities got together in Tiananmen Square and held a mass protest. The movement that was born at that rally (called, not unsurprisingly, the May Fourth Movement) was the first true nationalist movement in China and has consequently served as an inspiration for Chinese patriots of all shades, stripes, and ideologies since.

In the early 1920s, Dr. Sun Yat-sen, as the leader of the (up-to-then unsuccessful) Nationalist Party (KMT), accepted Soviet aid. With the Communist help, Sun Yat-sen was able to forge an alliance with the fledgling Chinese Communist Party (CCP), and started the task of re-unifying a China beset with warlords.

Unfortunately, Sun died of cancer in 1925. The leadership of the KMT was then taken over by Chiang Kai-shek.

After Chiang took over the KMT, he launched his famous "Northern Expedition" -- all the way from Guangzhou to Shanghai. This unified Southern China and, more importantly, let the Nationalists control the Lower Yangzi. Once they got to Shanghai, Chiang, who had never liked the Communists anyway, launched a massacre of CCP members. Among those who managed to escape the carnage was a young communist named Mao Zedong.

The Communists were forced to abandon their urban bases and fled to the countryside. There, the Nationalist forces (aided and abetted by German 'advisors') tried to hunt them down, and in the words (more or less) of Chiang, "eliminate the cancer of Communism." In 1934, the Nationalists were closing in on the Communist positions, when, under the cover of night, the Communists broke out and started running. They didn't stop for a year.

This was the Long March. When the Communists started, they had 100,000 people. A year later, when they finally stopped, they had traveled 6,000 miles, and were down to between four to eight thousand people.

Part of the problem is that they didn't know where they were going. They started in Jiangxi Province, about 400 km northeast of Guangzhou. Then they headed west, past Guilin, and into Yunnan Province, in southwest China. They would have stopped there, but the local warlords weren't really happy about having them. At Kunming, the capital of Yunnan Province, they turned north, past Chengdu in Sichuan Province, and eventually ended up in Shaanxi, near Yan'an. From then on, being a Long Marcher was the mark of aristocracy in the CCP. Deng Xiaoping, the former paramount leader of China, was a Long Marcher. With Deng's passing, there are few, if any Long Marchers left in the Party elite.

While in Yan'an, on the periphery of Nationalist power, Mao consolidated his position (gained during the Long March) as the sole leader of the Revolution. The classic book on this period is Edgar Snow's Red Star Over China, which includes some texts by Mao himself.

While all this was going on, the Japanese were busy occupying Manchuria. This proved helpful for the Communists -- the troops sent by Chiang to the North to contain and eventually eliminate the CCP much preferred to spend their time fighting the Japanese. In late 1936, Chiang's own generals kidnapped him and held him captive until he agreed to fight the Japanese before fighting the Communists.

In 1937, the Japanese invaded China proper from their bases in Manchuria, using the notorious "Marco Polo Bridge" incident as an excuse. Once whole-scale war had been launched, it didn't take the Japanese long to occupy the major coastal cities and commit atrocities. By the time that the war had ended in 1945, 20 million Chinese had died at the hands of the Japanese. The Nationalist Government fled up the Yangzi to Chongqing from Nanjing.

In 1939, World War II started. This initially had little effect on the situation in China, as the Japanese were not involved with war in Europe. However, after the attack on Pearl Harbor in 1941, the main thrust of the Japanese war effort turned away from fighting the Chinese and towards fighting the Americans.

After the Americans entered the war, the Communists started to consolidate their control over North China in preparation for the resumption of the civil war that would occur after the Japanese had been defeated.

The Nationalists, in contrast to the Communists, were disorganized and corrupt, problems that would only intensify after the war. Moreover, their attempts to fight the Japanese were ineffective at best. The general in charge of US efforts inside China, General Stillwell, lobbied Washington (ineffectively) to channel some aid to the Communists; this was not because Stillwell was sympathetic to their cause but because the CCP, employing guerrilla tactics they had independently developed during the civil war, was simply doing a better job fighting the Japanese than the Nationalists.

At the end of World War II, the war between the Nationalists and the Communists started up again. The Communists were hampered by the fact that the Japanese were under orders to surrender only to the Nationalists, not the Communists. This, however, did not end up making much of a difference. By early 1949, the Nationalists were hamstrung by intractable corruption and huge debts; they paid off their debts by printing more money, which only led to hyperinflation.

By that October, the Nationalists had fled to Taiwan and Mao Zedong had proclaimed the creation of the People's Republic of China. Curiously, while the Red Army was busy re-unifying the south, they didn't bother re-unifying either Macau or Hong Kong, even though it would have been extremely easy, and neither Britain or Portugal would have been in much of a position to protest.