In the last two centuries, Buddhism has undergone a number of changes, and has had to respond to a range of pressures, coming from:
Colonization of Asian countries by Western powers, which undermined political structures associated with Buddhism, but also led to Western scholarship on it, so helping its spread to the West, and to stimulating changes in Buddhism, both in colonized countries and in those influenced by them.
Christianity: criticism of Buddhists by Christians was one element in stimulating increasing Buddhist social activism. Moreover, in South Korea and to some extent the Republic of China, Christianity and Buddhism are currently rivals for people’s commitment.
Communism: this has been something of a wet blanket on Buddhism in China (now including Tibet), North Korea, Vietnam, Laos, Cambodia and Mongolia. It remains most repressive in North Korea, though Cambodia and Mongolia have escaped from its rule in the last twenty years.
Marxist-nationalism in Burma: not anti-Buddhist, as such, but it acts against Buddhist values.
War or its after-effects, especially in Cambodia and Sri Lanka: Cambodia was affected by American bombing, then by the Khmer Rouge; Sri Lanka has been affected by a civil war between the Sinhalese and Tamils.
Modern capitalism: originally brought with colonialism, though Japan developed its own capitalism as a foil to Western colonial threats. This has brought greater prosperity to many, but also undermined traditional value-structures.
Consumerism: a particularly virulent form of capitalism, currently perhaps the greatest corrosive force undermining Buddhism in Japan, South Korea, Taiwan, Thailand and more recently mainland China. Its commodification of life and emphasis on possessions has heightened elements of greed in human nature and it accordingly encourages a reorientation of values.
Modernity: democracy, egalitarianism, secularization, improved communication and ease of travel.
Buddhist monarchs still exist in Thailand, Bhutan and now again in Cambodia, and Buddhism remains the dominant or largest religion of Sri Lanka, Thailand, Burma, Cambodia, Laos, Vietnam, Bhutan, Tibet, Mongolia, China, Taiwan and Japan. It retains a strong presence in South Korea, and is reviving in Nepal and on a small scale in India. Outside Asia, it has broken entirely new ground.