The Pacific is the largest ocean, stretching from Australia and New Zealand to the American west coast, and in 1750 this ocean was virtually unexplored.
This huge area might be unexplored, but it is certainly not empty. 31 tribal nations are spread out over a large amount of island groups, Australia, and New Zealand, while colonial nations hold some ports on the fringes of these vast regions. Additionally there are a great number of unexplored and unpopulated islands that are suitable for colonization.
To be part of one of the Polynesian or Micronesian nations means that the distances to neighbours are vast and the sailing crafts or canoes are small. These nations are small in economics and population, but this applies to all, so it is no barrier for expansion.
Nations from the developed world might enter the region and conquer islands, which might generally not be that hard, but economically the distances and resources hardly make it worthwhile. Adventurers might also enter the region to explore, make maps, buy exotic items, find unpopulated islands and perhaps join a native nation.
Island nations can attempt to gain technology and upgrade their ports, ships, weapons and businesses, if they can gather enough funds to do so. Some island nations might develop into local powerhouses that dominate vast stretches of ocean.
In Australia, apart from one British port, three major Aboriginal tribes are at home on the continent and there are enough uninhabited sites for new ports. If the Aboriginals would desire to organize, they can adopt new technology and attempt to develop Australia into an independent nation, free of European influence.
On the New Zealand islands there are six Māori nations, while no other nation has as yet settled there. The indigenous nations have an opportunity to unite and create a strong union against invasion and in favour of expansion.