what are the social and economical factors that led european civilization go through some major changes between 11th and 14th centuries ?

This period in history is all about the fall of the feudal system and the rise of the middle classes. There were a number of key factors but I will outline two here:

The Crusades.

The first crusade was called by Pope Urban in the 11th century. In order to meet their Christian obligations (and pursue the possibility of booty) many European noblemen liquidated their assets, including vast tracts of land. They needed the money to buy equipment and to pay mercenaries to accompany them. This allowed some of the up and coming middle classes (successful merchants, soldiers etc) to buy not only land but also sometimes titles. The crown often auctioned off land and assets belonging to those landed gentry who were killed, along with their heirs, while on crusade.

The Plague.

Some estates in Britain (probably the rest of Europe too, but Britain is my speciality) were hit so hard by the plague in the 14th century that they could no longer function, they had lost too many of able bodied labours. This meant, that in a country where serfdom was the norm, labour was, for the first time, actually worth something. It didn't take long for healthy labourers to realise that their ability to work might be worth more elsewhere. There were nobles willing to bid for workers and workers willing to reject their former social obligations to land and move.

Thus social mobility was born.