Answer:
Unfurled banners means "banners that are unfolded and spread out"
Explanation:
This means that Columbus claimed the islands for Spain by public proclamation and "spreading out banners" i.e likely spreading out their flags as a sign of conquest over the islands.
This state of "unrolling or spreading out banners" is used to show solidarity and also conquest. This can be seen when flags are spread out and lifted high.
