During the buildup to the French and Indian War, Britain sought more land in North America primarily to support the rapid population growth of the British colonies. The colonies were experiencing significant population influx, driven by factors such as immigration and high birth rates. This growth created a pressing need for more agricultural land and resources to sustain the expanding population.
While the lack of good seaports and agricultural limitations in some regions were factors that influenced colonial expansion, the overriding motivation was the desire for land to accommodate settlers and agricultural development. Establishing a territory for Indigenous Americans outside of British colonies was not a major objective for Britain; rather, the British often sought to control territories occupied by Indigenous peoples to expand their own colonial footprint.
In summary, the primary impetus for Britain's desire for more land in North America was to facilitate the growth and sustainability of its colonies amidst a rapidly increasing population.