Why did capitalism, slavery and colonialism come together in Western Europe at the end of the middle ages ?
The usual story is that the expansion of the Ottoman Empire, dramatised by the fall of Constantinople in 1453, constricted the trade routes to the more advanced societies in the East, motivating the 'voyages of discovery' search for new trade routes - and trade was already detached from the relatively self-sufficient and stable rural social formations we know as 'feudalism'. The UK, being an island nation at the western fringe, seafaring for both food and defense, occupied the preeminent position for this development. The inflows of capital from slavery and colonialism then recursively facilitated capitalism, urbanisation, and ultimately industrialisation.
There is much truth in this picture, but in his 'Brief History of Equality' Thomas Piketty adds a new insight. Applying Adam Smith's contemporary description of an effective capitalist economy, Piketty finds that in fact both Chinese and Ottoman societies were more 'capitalist' at the inception of the industrial revolution. So what really made the difference in Western Europe ? Piketty's answer is centuries of European wars - that had forged more command-and-control establishments, bigger navies, better weaponry, etc - in short: military force, and the ability/willingness of Europeans to use it.
I'd add another point Piketty might well have missed (because the French tend to have a view of race different from the anglophony): the specific form of racial slavery the Europeans perpetrated was more extractive than the land empires of the Chinese and Ottomans, enabling even more exploitation, brutality - and capital accumulation. Which in turn gives rise to a scary question: is the 'othering' of different peoples not just an essential feature of fascism - but of capitalism ?