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He will be remembered as one of the most incompetent leaders of the 20th century.
He was extremely corrupt, arrogant, and brutal. Back when he controlled all of China in the 1920s, he greatly weakened the country by ordering a massacre of communists and leftists in the united government, which destroyed the carefully brokered relations that his predecessor had established. It fragmented China and killed the extremely rapid economic growth of the late 20s, and China spent the next decade stagnating and weakening in a civil war, which likely enticed Japan to seize the moment of weakness and invade.
The KMT efforts against Japan were bad, with CKS literally being kidnapped by his generals because he was ignoring the ongoing Japanese invasion to focus on killing communists. Under his orders, the army breached dikes on the Yellow River and caused an enormous flood - with no warning to the civilians - that killed up to 1 million of their own countrymen, and displaced another 3 million just to slow the Japanese advance. The real kicker is that Japanese forces weren't even in the area, and the advancing troops just went around the devastated towns and cities. Even during the war against Japan, CKS and his chronies embezzled hundreds of millions of dollars worth of American aid.
It was this corruption and and uncaring brutality that led to the resurgence of the communist party after they were nearly completely wiped out. Even Taiwan, recaptured after WW2, was treated savagely. CKS lost the trust and confidence of the people, entire army divisions defected to the CCP, and he was an international pariah that sabotaged his own talks with both the Americans and the Soviets when they expressed an interest in helping him secure power for no fucking reason.
After being expelled to Taiwan, nothing changed. His regime brutalised the local people, and corruption and racism was rampant. Our national identity's 'founding moment' is the armed uprising/resistance against the KMT dictatorship.
One of his last great acts to fuck the people of Taiwan over was the diplomatic tantrum you mentioned. The UN was ready and willing to recognise the Republic of Taiwan, and the CCP would have agreed to get their much coveted recognition. Instead, he ordered the total walkout of the ROC's UN delegation from the negotiations, and then pulled the ROC out of the UN completely in protest. Everyone promptly shrugged and gave China the seat with no deal for Taiwan. CKS' incompetence is so staggering that he's still fucking us hard from the grave.
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