It was necessary for the United States to annex Hawaii because there were few lands left to colonize. By the time the United States worked out that it might be a good idea to expand her territories, there were very few countries left to claim. Most other countries had been claimed by Great Britain, France, Spain, Portugal and Germany. It also made sense to annex Hawaii as it is relatively close to the USA. The kingdom of Hawaii was originally an independent kingdom with its own ruling monarchy.
The Emancipation Proclamation only freed the slaves that were in rebelling states. It didn't free the slaves in the North or effect the border states at all.
