Short answers, pulled from the story.
Western imperialism in Asia was the influence and colonial domination of Asian territories by Western powers, peaking from the 16th century and substantially reduced by 20th century decolonization. It originated in the 15th century search for trade routes to the Indian subcontinent and Southeast Asia after Ottoman control of the Silk Road. It formally ended with the independence of Portuguese Macau in 1999.
Western imperialism in Asia originated in the 15th century search for sea routes east and peaked from the 16th century colonial period. It spanned roughly six centuries and formally ended with the independence of Portuguese Macau in 1999.
Portugal first dominated Indian Ocean trade after winning the battle of Diu in 1509 against a joint Mamluk and Arab fleet. Afonso de Albuquerque conquered Goa in 1510 and captured Malacca in 1511, building a maritime empire to monopolize the spice trade.
The British East India Company gained control of India through victories such as Robert Clive's defeat of Siraj ud-Daulah at the Battle of Plassey in 1757, followed by the Anglo-Mysore and Anglo-Maratha wars. After the 1857 Indian Rebellion, the company relinquished its role in 1858 after 258 years, and Lord Canning became the first viceroy of India.
China signed the unequal treaties after military defeats by Western powers, beginning with the First Opium War with Britain in 1839. The 1842 Treaty of Nanking ceded Hong Kong Island and opened ports, and the 1858 Treaty of Tientsin opened the interior and allowed Christian missionary work.
Japan responded to Western pressure after Commodore Matthew Perry sailed warships into Edo harbor on the 8th of July 1853, leading to the Convention of Kanagawa on the 31st of March 1854. The realization of technological weakness led to the Meiji Restoration of 1868, after which Japan industrialized and became an imperial power, defeating Russia's navy in 1905.
Western imperialism in Asia ended through decolonization after World War II, when wartime Japanese occupations shattered European pre-eminence. Britain granted India and Pakistan independence in 1947, the Netherlands ceded Indonesia in 1949, and the final European political control closed with the return of Portuguese Macau to China in 1999.