So many underdeveloped countries has been suffocated with marginalization and bad governance which has resulted to the impoverishment of the citizens where by making them to be less useful to the society and also left them with no option than to endulge in violence and division that might take many years to be curtailed.
You have just identified the major problem of most underdeveloped countries. Corrupt leaders are controlling the political system of these nations with their evil cronies. The only solution is to conduct free and fair elections where citizens can vote for perceived good leaders and vote out bad ones. If these politicians know that the people will vote them out if they fail to fulfill their campaign promises, they will sit up.
I think it will make sense if the colonial masters or the developed countries in general come to the help of this country not by reaching on a selfish agreement with them for something in return but by putting every force on ground in achieving a good leadership for the country,
Colonial masters also have problems in their homeland they want to solve. So every nation should be able to handle its problems. Most of these colonial masters benefit from the underdevelopment of their colonies so they will never want to assist them fix their economic problems. Developed nations use underdeveloped countries as markets for their finished goods and natural and human resources sources.
political office has to be made less attractive to accommodate technocrats in the system to salvage the horrible situation of the citizens of the country at large to be propagated in line with good governance also by Brick tightening all the lope holes where public funds can be embezzled or syphoned by the office holder.
My country's lawmakers are one of the highest paid in the world while we are among the poorest in the world. The people that will make laws to make laws to make these political offices unattractive are benefitting from the system. So they will never make such laws. The only solution is to elect sincere leaders that have the intention of serving selflessly.
Note total scrutiny of individuals either by investigating them secretly to know more about them or even go as far as knowing much about their source of wealth as the case may be before allowing them to contest for the particular position they are interested in.
A system that promotes vote-buying will always produce criminal politicians. We don't need to scrutinize the source of their wealth for voting purposes. Corrupt individuals should be arrested, tried, and sent to jail if they are guilty. That's why the judiciary should be independent.