Rejectionist isolationism was broken by Western military force.

Evidence

China’s rejectionist policy was in large part rooted in the Chinese image of itself as the Middle Kingdom and the firm belief in the superiority of Chinese culture to those of all other peoples. Chinese isolation, like Japanese isolation, was brought to an end by Western arms, applied to China by the British in the Opium War of 1839–1842. — Samuel P. Huntington, The Clash of Civilizations and the…, 195