Sentence:  In late 1957 the M.P. ( Mouvement Populaire ) appeared and in the spring of 1958 the internal <WSD>strains</WSD> of the Istiqlal was revealed when the third Council of Government under Balafrej was formed without support from progressive elements in the party . 
Meaning of the word marked with <WSD> tags:  (physics) deformation of a physical body under the action of applied forces