To suggest it was any sort of paradise before is beyond disingenuous.
Agricultural + paradise - strange combination of words - the fact is the country has the capacity to produce food and much much more. It has never lost that potential, although it may have lost it's market. It is not a situation where it was once a desert, then an oasis.. What you refer to is a 'paradise' - which is an entirely different notion that includes the human element of pleasure, well-being, opportunity and prosperity. It was a paradise for some (fill in the sector of the people you meant here), at the same time that it's southerly neighbour was a paradise (and still is for some ...). Israeli is an oasis (to use Obama's description) and a paradise for - but who?
Zimbabwe's potential under colonialism was stunted for the benefit of the colonisers' investments into mining and agriculture. After liberation, human development has advanced in leaps and bounds, although the economy has not.
The result of all that, is the disproportionate poverty, factionalism and political upheaval we still see today. Here are the facts as I see them: There was a war of liberation - destabilising domestic and foreign forces remained in play in the nation, and are a constant force today.