It seems that oftentimes countries that are always a mess tend to blame European/U.S. colonizers for their current situations.
There is a vital question missing: What is a country?
It's an artificial construct: borders are drawn and redrawn arbitrarily, after war, every skirmish and every conflict between two empires. Most of the borders that exist today were different a hundred years ago. Many, if not most of the people living in many, if not most, modern countries do not have ancestral roots in that geographical region or blood-ties in their present community, or history under the present form of government.
When you say "a country" does something, do you mean the people or the present government, or merely the present head of government. They're not always synonymous or even in accord.
And when you talk about colonization, you have to remember that it didn't last from one date to another date and then end: colonization wiped out entire populations and relocated others, re-assigned territory, changed borders, altered the landscape, eradicated species and types of agriculture, rerouted waterways and disturbed ecosystems. Its effects didn't move out when the last British civil servant packed up his typewriter. White planters, mine-owners and industrialists remained behind and went on controlling the economy. Now they same people or their descendants are doing it long-distance, through trade, loans, aid and arms supplies.
If they were doing well they would have been able to resist colonization.
The questions missed here: Relative size. Relative aggression level. Weapons technology.
You're essentially saying that if Belgium had been prosperous, it wouldn't have fallen to Germany in 1914 and the Sioux should have been able to stand against attack after attack by the US army for 50 years.
The U.S. and European nations were under attack at various times and had to defend themselves.
The US was never attacked. It attacked others, and suffered only a couple of small, ineffective retaliatory strikes, except for Pearl Harbour, and they goaded Japan into that action by blockading its fuel supplies in '43. Europe was last occupied by Muslim empires c. 1500. All its other wars were internecine, over matters of succession, territorial expansion, resources, alliances and religion. Those wars didn't change the ethnic makeup or economic capability of modern European nations.
Other countries were attacked, colonized, later resisted and are now doing well.
That's not under the population's control. The one that got the river in the final treaty is doing better than the one who was given the arid highland; the one whose railways and bridges were blown up needed a loan and is now in thrall to an arms-dealer; the one whose colonists poisoned the river with gold-mine tailings is worse off than the one whose forest were were burned off for the coffee plantations. Colonists may go away (though a lot of them stay and hold on to the loot: see South Africa) but their damage remains.
Is the colonial history of a country that has never done well since the end of the colonial period really a large factor for their current situation?
Is history a factor in the present state of affairs?
Venezuela has oil and is a mess. Argentina, which is a great country (potentially) is always a mess. Mexico never really improves its situation. Most of Central America is a mess. Actually, most of the world is a mess.
Jillionnaires are good at making messes.
https://depts.washington.edu/chid/i..._Conflicts_in_Latin_America_and_Water_Law.pdf
World-dominating political and military powers are good at making messes.
https://mic.com/articles/92581/how-...a-in-7-classic-historical-cartoons#.y6szEPYNe
https://en.wikipedia.org/wiki/The_Great_Game
Um...it's complicated.