Which countries are you referring to? First of all borders in Europe were not the way they are right now 150 or 200 years ago.
Second, an example for a tiny country that was exploiting an african nation well into the 20th century is Belgium [1]
It's the next sentence: Germany, Austria.
Belgium indeed went on a bit of an exploitation spree. But it's never been notably wealthier than its neighbours. (Of course the king got some nice palaces, but that's not country-level wealth.) Instead the industrial part of Belgium was wealthy in the same era that the nearby industrial part parts of France were (and Detroit was). Now that's rust-belt poor, and the wealthy bits are tracking Holland. These patterns seem hard to explain by referring to the (very real) evils of the congo empire.
- What is now Belgium was one of the wealthiest parts of Europe in the Middle Ages, long before any colonization.
- Belgium was the second European country to industrialize. This caused the economy to boom and Belgium had the 4th highest GDP in 1900. Congo was only a colony since 1908.
- In 1918 the whole economy was destroyed because of the war. The Germans had plundered the country. Whole factories were dismantled and shipped to Germany.
- In 1945 the economy was once again destroyed because of the Germans.
- In 1956, at the heigh of colonial exploitation, Congo was 3,3 % of Belgian GDP and 75000 direct and indirect jobs. Not nothing but hardly the base of all wealth. It was much lower in the preceding decades.
- Congo became independent in 1960. Annual GDP growth rates were much higher during the 60's than during the whole colonial period.
I would say Belgium is currently wealthy because of the Marshall plan.
source: https://www.cambridge.org/gb/academic/subjects/history/twent...