"Surely a country’s positionality in the global system contributes to how much violence occurs within their borders?"
Surely, but how much? 1 per cent or 40 per cent? We don't know. As you say, nothing is a closed system.
For example, by 1949, China imported Marxist-Leninist-Stalinist school of thought, a totally culturally alien system constructed by (mostly long dead) Europeans, which was the root cause of the horrors of the Maoist era - none of which were imposed by external empires by force. For all its faults, the US never forced the Chinese to exterminate the sparrows or attempt to build a steel mill in every village, resulting in a massive economic collapse and death toll.
China had many famines before that during the century of humiliation. Maoism was itself a reaction to the dire social conditions of the time.
This doesn’t absolve Maoism of its policies which led to millions dying. (And yet we shouldn’t absolve the global capitalist system either which leads to millions of preventable deaths each year.)
Colonialist exploitation has been major historic driver over this timeframe (shifting to neo-colonialism in the world system post WW2). Admittedly it hasn’t been the only one. But our understanding of world history loses nuance if we gloss over colonialism and neo-colonialism over this period and treat historic events as due to the supposedly essential traits of this or that nation.
Political system may be one of the reasons (feudalism doesn't have a great record in preventing famines either), but the most salient explanation might be that a pre-modern economy with high density of population is inherently prone to famines - a bad drought will easily topple the precarious balance between demand and supply towards lack of food, and without a railway network it is nearly impossible to move food easily among places that don't have good ports.
I thought we were talking about the role of colonization in violence in China over the past 250 years. Most events you listed (Taiping rebellion, Boxer rebellion, CCP-KMT civil war) were the result of weakening of the Qing dynasty by foreign powers, its downfall, the chaos this produced during the Warlord era. The Great Leap Forward and Cultural Revolution (again I’m not exonerating them) were themselves in large part reactions to the legacy of imperialism on China.
Generally under colonialism, the colonial power actively prevented any development of native capitalism in the colonies, even if the colonial power was capitalist in their home country. The goal was to prevent the colony from developing its own economy and rather to have the colony supply basic resources (food, minerals, oil, etc.) to the colonizer and force the colony to rely on goods from the colonizer.
It’s worth considering the famine in India at the end of the 19th century. The British integrated India into the world capitalist system in a way that directly led to famine: promotion of cash crops which led to vulnerability when drought struck; speculators hoarding food during famine (some stores of food even rotting while people starved); building of railways and ports (which were used to export food out of famine stricken areas for profit); and laissez faire relief policies. The death toll was in the millions. I found Mike Davis’ book Late Victorian Holocausts to be a good resource on this subject.
While the famines were real, and a result of British rule, that wasn't because India was part of a "world capitalist system". Capitalism doesn't just mean "people doing things for profit" but rather the use of capital to build up industry, which Britain had no intention of doing in India.
Capitalism is a system where one class of people (workers) sell their labor for the profit of another class (owners/capitalists). So feudalism was neither capitalist nor industrialist. Colonial capitalism - not typically industrial but still capitalist. Industrial capitalism - both industrialist and capitalist. The modern American economy - service based not industry based - but still capitalist.
Surely a country’s positionality in the global system contributes to how much violence occurs within their borders?