Why was the marshall plan effective?

The goal of the Marshall Plan was to rebuild the shattered countries of Europe, and restore them to pre-war prosperity. It aimed to feed the people, rebuild destroyed economies and turn Europe from the cataclysm it was to a functional continent. 

As of 2016, Germany and Italy, who fought some of the war's bloodiest battles, are now among the world's richest. France, Great Britain, Germany, all have very little starvation. Their cities have been rebuilt. Their economies revived

if interdependence implies a two-way dependence, and if each partner is equally dependent on the other for success, then there is an equal commitment to the making the partnership successful. the advantage is sustainability of the relationship, the disadvantage is that decisions are "democratic" and therefore may take longer to reach and more likely to be a compromise (which is not always the best solution). as the interdependence moves away from equality, the decisions become more influenced by the more independent partner. in the extreme the relationship becomes more dictatorial and more like "master-slave". generally the relationship has less commitment in both directions and is more likely to be temporary.

if one generalizes (and one shouldn't), equity partnerships, which is probably what is implied by interdependence, can be slow to progress or change but durable. the extreme alternative, independent-dependent partnerships tend to be efficient but more fragile.

hope this but you will have to site your own evidence. : )

i think you really need to revive you answer! : d