The Anglo-Chinese War was a conflict from the rise of the ROC in 1989 until the British victory in 1991.
The Chinese had always claimed Hong Kong, a former port city that had been under The British Empire since the 1840's. It wasn't until the collapse of the Qing Dynasty in the mid-late 80's that the Chinese had the tech and means to make this claim more enforceable. Chinese troops crossed the border into Hong Kong just 2 weeks after the Republic had become a nation. The Chinese peacefully annexed Macau at the Lisbon Conference as Portugal didn't want a war over their last colony anyway. The war would begin as soon as news of Hong Kong's invasion reached the British.
The Anglo-Chinese War (1989-1991)
The British, however, had other ideas and once they heard of the Chinese invasion they sent over 100,000 troops to Hong Kong. The troops soon retook Hong Kong as the Chinese assumed the British would be like the Portuguese; but they were wrong. The Hong Kong People's United Army (HKPUA) held some of the smaller ports until British troops could arrive. Just a mere few days later British troops marched through Hong Kong with very minimal resistance, do to the Chinese not thinking the British would invade. Britain pushed even further than Hong Kong, however, taking all of Guangzhou and formerly annexing it. In 1991, under threat of further actions by the British, the Chinese surrendered.
End of The War and Post-War
The treaty of Shanghai is signed and states that the Chinese will give the British Guangzhou, however the British must make it a Dominion with at least some self-governance; Hong Kong will be made part of and also the capital of the Dominion of Guangzhou. Macau is made a "special region" of the Dominion do to cultural differences. China will pay the British just 10,000,000 dollars in war reparations. The war ends with a new Dominion and a more humble and less powerful China. The Royal Army of Guangzhou is created with just over 50,000 men in it's ranks, well a separate army for Macau (The Army of Macau) is created, but has just 2500 men, so it is partly under the Guangzhou's defense.