[J]ust because you believe colonialism is the only reason why developed countries are developed it doesn't mean your premise on its persistence is true.
I just came across the following segment recently, and I posted it to the 'Two Forms of Socialism' thread. It's relevant here.
The initial resources for capitalist development in England, its birthplace, came not from entrepreneurial individuals saving their money and then applying it to production, but from looting and plunder internationally, inherited fortunes, and the stripping of the mass of the population of access to the means of production and their transformation into a propertyless class with nothing to sell but their labour power.
And the course of capitalist development soon swept aside the independent entrepreneur. This took place through two processes: first, the inexorable logic of competition, which is not to perpetuate competitive struggle, but rather to compel each producer to drive out his rivals, with the aim of becoming a monopoly; and second, the expanded scale of production, which meant it could no longer be organised by individual entrepreneurs, but required the mobilisation of capital by corporations resting on a vast credit structure.