Not only was Venezueala wealthy before Chavez, it ran proper elections. Its balanced, stable democracy reflected its population's will.
The unfortunate truth is aloof upper/middle classes ignored Venezuela's poor. The latter got pissed off and, on their own volition, voted in a demagogue who then tore apart the country. Many problems in Latin America find origin in American meddling. Venezuela, today, is not one of them.
[1] http://americasquarterly.org/content/venezuela-chávez-anatom...
1) the US manipulated, deposed, and built governments there for the last century, often triggering or at least backing civil wars. Much of this was done to further corporate interests, like The United Fruit Company.
2) During the Cold War, the US convinced the governments of the regions to retool their militaries as counter-insurgency forces to counter communist rebels.
Those set the stage for any number of oppressive regimes and wars.
The rise of Chavez could be seen as obvious, given the above, but Venezuela's specific problems today are due to Chavez' party and his successor.