Martin Luther King, Jr, campaigned for the extension of civil rights to (= for them to include) black people. The extension (= increasing) of police powers in the province has been heavily criticized. His report contained serious criticisms of the finance director, and, by extension (= therefore), of the entire board of management. The article is an extension of (= takes further) the ideas Professor Fox developed in an earlier book. I've applied for an extension to my visa (= asked for it to last longer). They are hoping to get an extension of their loan (= to be given a longer period of time in which to pay it back).