with the criterias or principles which was used in the reconstruction and restoration processes after the ww2
The criteria were often ideological - e.g, communists didn`t care about tenement houses from 19th/early 20th century as having capitalist background and atmosphere. They prefered to have older architecture rebuilt. Even churches, which always surprised me. But we should remember that it wasn`t only communists but primarily pre-war architects who led the reconstruction - they were supervised by communists but often managed to implement their own ideas.
Another difficulty apart from politics was the lack of funds, labour and contruction materials. E.g., Warsaw sucked in bricks from other cities which weren`t reconstructed, mainly ex German ones.
I don`t know much about similar ideological tensions in Syria - the main problem will be money - Syria is ruined and has scarce income. International help will be a must.