Back in the 1600s, didn't Belgium have one of the strongest economies in the world?
I don't think Belgium had a strong economy till the early 1800's, let alone was recognized. (You're thinking of the Netherlands I bet)
They benefited quite a bit from the 1st and 2nd industrial revolution, and had a successful overthrow of the monarch in 1848 to establish a constitutional monarch.
Then Leopold II came into power, and sparked the new wave of imperialism by claiming the whole motherloving African Congo for the rubber.