An understanding of historical and dialectical materialism. The contradictions within capitalism simply cannot continue forever, just as no previous political economy could continue forever.
Granted, another possibility is that capitalism literally destroys the world.
It isn't. The only thing that's inevitable is the end of Capitalism.
Freeman and slave, patrician and plebeian, lord and serf, guild-master and journeyman, in a word, oppressor and oppressed, stood in constant opposition to one another, carried on an uninterrupted, now hidden, now open fight, a fight that each time ended, either in a revolutionary reconstitution of society at large, or in the common ruin of the contending classes.
What is the actual basis for thinking communism is inevitable
An understanding of historical and dialectical materialism. The contradictions within capitalism simply cannot continue forever, just as no previous political economy could continue forever.
Granted, another possibility is that capitalism literally destroys the world.
It isn't. The only thing that's inevitable is the end of Capitalism.