There are no incidents of Chan or Zen-led military conquests of other lands, nor have there been any great Chan or Zen explorers to claim new territories in the name of their religion.
In Japan, there have been a few cases in which conflicts between Zen and other Buddhist sects have lead to violence. For example, Nonin's Zen monasteries were destroyed by monks and followers of Kofukuji, a monastery of the Hosso Buddhist sect. This occurred during the course of infighting between Kofukuji monks and those of several other monasteries caught up in alliances between warring political clans. Nonin's group appears to have been caught in the crossfire, but was vulnerable because his fledgling Daruma school had been banned by imperial authorities in 1194, and because negative accounts had been written about the school and its master by prominent Buddhist leaders.
Another example of sectarian in-fighting occurred in Japan during the Muromachi period (1336-1573). The Ashikaga clan, which had assumed power only a few decades before, hoped to make Zen the official Buddhist sect and therefore formed an alliance with its leaders. In 1368, the monastery was allowed to build a tollgate and collect the revenues. There was an escalation of hostilities between this and other monasteries, and Tendai monks launched extended protests in the capital. Ashikaga leaders finally agreed to banish two prominent Zen monks and demolish the tollgate. While Zen did not become the official sect, it did benefit in a variety of ways from the support of the Ashikaga clan and was the dominant form of Buddhism during this era.
More common in Japan, and also in China, were anti-Buddhist movements directed by the government toward all of the Buddhist sects. Usually of short duration, but devastating in their destruction, these incidents were connected to political situations, often occurring when Buddhism was in danger of becoming too wealthy or too powerful—or too great a drain on the royal coffers—or when it was perceived as a threat to the government.
Outside forces were more influential in the 19th and 20th centuries, as Buddhist organizations in China and Japan were affected by massive social, political, and cultural changes resulting from contacts with the West. In the mid-19th century, the British, French, and the United States waged a series of wars over the right to sell opium in China. The Qing government was opposed to the opium trade as it created severe economic and social problems. In defeat, China was forced to relinquish territory and to open ports and port cities to westerners, among them Christian missionaries as well as traders. Weakened by these events and others, the Qing dynasty was overthrown early in the 20th century.
After the fall of the Qing, a prolonged civil war broke out between opposing factions. In 1949 the Chinese Communists prevailed. After a century of foreign invasions and two decades of civil war, the country was in shambles. With the advent of communism as a political ideal, Buddhism, like all religions, came under severe criticism. Religion was an ideological threat ("the opiate of the people") and it was also a political threat as it represented a form of authority that could and sometimes did oppose governmental powers. Most importantly, Maoist land reforms confiscated revenue-earning property from the monasteries.
In Japan, in 1854, American ships sailed into a harbor at the entrance to Tokyo Bay and forced the Japanese government to sign trade agreements. This was a major factor in the defeat of the Tokugawa shogunate and restoration of the Meiji emperor in 1868. In response to western movements into Asia, Japan decided to form a "Greater East Asia Prosperity Sphere," believing that domination from within Asia would be preferable to domination by the West. It began to take control of territories adjacent to China, including Manchuria, Korea, and Taiwan, and then threatened China itself. In the 1930s, Japan launched a series of attacks on China, defeating and occupying Hebei and Nanjing. During World War II, Japan took control of more territory, including Thailand, Burma, the Philippines, Macau, Hong Kong, and more. While most of these events did not involve Chan or Zen specifically, the repercussions would affect both, and all of Buddhism in East Asia, in a variety of ways.
One final series of conquests relevant to Chan took place in Vietnam. Until the Lu dynasty (1109-1224) Vietnam had been controlled by the Chinese empire, and Chan, called Thien in Vietnam, was introduced very early as part of the Chinese cultural influence. In the mid-19th century France colonized Vietnam and made it part of French Indochina. The colonial government encouraged the spread of Christianity, and efforts were made to suppress Buddhism. During World War II, Vietnam was freed from French control and occupied by the Japanese.