They had great military strength, grounded in their technological edge, despite being poorer in natural resources than India and the Congo.
India and the Congo weren't really countries when the Europeans showed up: what we now think of as those countries had vast collections of tribes more than anything else. They hadn't (and to some extent still haven't) undergone the unification that many European countries were undergoing or had undergone when colonization started.
Even England had problems with Scotland and Wales up until relatively recently, and problems with Ireland up until about ten years ago.
Are you extrapolating that the key was not the technological edge, but strong central government? I'm not persuaded.
(a) Some of the colonial powers were small tribes or collections of tribes themselves. England is one example, as you say, but Belgium and Portugal are surely the poster children for this. Spain is still a vast collection of tribes more than anything else.
(b) Some of the colonized regions had strong central government, notably the Inka empire Tawantinsuyu.
(c) Forms of strong central government have existed in many times and places in the past (Carthage, the Roman Empire, arguably the Roman Catholic Church before Westphalia, ancient Egypt, Axum, China at some periods, Tawantinsuyu, the Maya empire) without kicking off an industrial revolution. Indeed, the argument has often been made that it was precisely Europe's lack of strong central government, together with the current state of philosophy, that permitted the Industrial Revolution to begin.
India and the Congo weren't really countries when the Europeans showed up: what we now think of as those countries had vast collections of tribes more than anything else. They hadn't (and to some extent still haven't) undergone the unification that many European countries were undergoing or had undergone when colonization started.
Even England had problems with Scotland and Wales up until relatively recently, and problems with Ireland up until about ten years ago.