Hier mal die Bezüge:
Unlike earlier travellers, such as Tupaia, Mai was destined to see his home again, being repatriated by Captain Cook during his third voyage of exploration to the Pacific.
Indeed, a sign of
how engrained (Mai, Tahiti’s people and the islands of the Pacific more generally)
were becoming in the global politicking of European nations
is provided by his return.
The return provides the sign of how ... were becoming ...
Ich kenne zu wenig vom Kontext, um dir das komplett zu übersetzen, aber vielleicht verstehst du den so aufgeschlüsselten Satz jetzt besser.