Between 1990–2000 the USA experienced its largest population increase since records began, totalling 32.7 million individuals. This represented a proportional increase of 8.2 per cent of the total population, bucking the trend of declining proportional increases each decade since the high of 18.4 per cent from 1950–60. The western states, and to a lesser extent the South, experienced the vast proportion of this growth. The two states with the greatest percentage increases, Nevada and Arizona, experienced high proportions of immigration from outside the USA, with most of this growth confined to a few large urban areas. This continued the trend of westwards movement of the mean centre of population that the USA has shown since independence, as technological advances make its western territories more habitable. In addition to this, counties bordering Mexico experienced much higher growth than those bordering Canada, highlighting the increase in both legal and illegal immigration across the southern border.
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