This paper analyzes the demographic processes that contribute to population growth and redistribution in a multiregional system using a new method. The method incorporates a historical perspective that can be used to trace dynamic population processes as they evolve over time. It uses an open multiregional projection model framework in identifying the contributions to regional growth made by each of the principal demographic components of change: fertility, mortality, immigration, emigration, in-migration, and out migration. At the same time, the method recognizes the importance of disaggregating the native-born and foreign-born populations. Available public data and indirect estimation techniques are used to develop the data inputs for the projection model, with which the regional population changes for each 5-year period between 1950 and 1990 were reconstructed. Regional growth rates for the foreign-born and native-born populations are partitioned into the separate demographic components of change, and the projection model identifies the separate contributions to regional growth made by each population. This allows a direct comparison of the impact of immigration with those of corresponding native-born contributions effected through internal migration and natural increases. Finally, the application of the method allows the identification of the contribution that 'recent' (post-1965) immigrant cohorts have made to the composition of the youngest age groups in each region, and also to simulate the impacts of zero immigration scenarios on regional growth.