Changes were not limited to new designations, as the interpretation of many existing National Historic Sites did not remain static and evolved over time. For example, the commemoration of National Historic Sites on the Prairies related to the Red River Rebellion and the North-West Rebellion has gone through at least three phases to date. In the 1920s, plaques erected at these sites trumpeted the expansion of Canada and western civilization across North America. Due to local pressures, changes at the HSMBC and evolving historiography, texts introduced in the 1950s avoided the previous triumphalist version of events, but also avoided any analysis of the causes or consequences of the events. Commencing in the 1970s, a changing approach to heritage conservation at Parks Canada, coupled with growing regionalism and a more assertive Aboriginal rights movement, led to the next generation of interpretative documents, one that included a focus on the societies which Canada's 19th-century expansion had displaced.