You are
Hans Island
I use to be one
But now that is done
Now I am feeling rationed out
The island, located off the coast of Greenland, was formerly a disputed territory, with Canada and Denmark laying claim to it. They have now agreed to split the island in two.
Wine party is over, bummer about
As part of the dispute, in 1984, the Danish Prime Minister planted a flag and reportedly left a bottle of brandy, which is a liquor distilled from wine.
Father is large, mother is small
The father is Canada, the larger of the two countries.
Both were once isolated and all
But with this, records stand no more
As of now, they share sides
Near top of the world
The island is located in the Nares Strait, approximately 80° north latitude.
I am visited sparse
The few who came were cheerful
Despite some being enemies
The island is uninhabited, with the only visitors being researchers and officials from Canada and Denmark, alternating visits to plant their country's flags and leave notes and liquor, laying claim to the island.
With a clink of sea salty glass,
I drink one last drink of change
And face my future destiny
To world peace!
On June 14, 2022, a treaty was signed by the Canadian and Danish governments, splitting the island between the two countries.