Why was the whole of ulster not partitioned into northern Ireland?

There were a number of reasons why the whole of Ulster was not partitioned into Northern Ireland.

* The wishes of the Irish people. The Irish people had overwhelmingly voted for independence from the United Kingdom in the 1918 general election. This made it clear that the majority of Irish people did not want to be part of the UK.

* The British government's desire to maintain control of Ireland. The British government was reluctant to give up control of Ireland, as it viewed Ireland as a strategically important part of its empire.

* The threat of civil war. The British government was also concerned that partitioning Ireland would lead to civil war between Protestants and Catholics.

As a result of these factors, the British government decided to partition Ireland, with the six counties of Northern Ireland remaining part of the UK and the rest of Ireland becoming the Irish Free State.

The partition of Ireland was a controversial decision that has had lasting consequences for the island of Ireland. The border between Northern Ireland and the Republic of Ireland remains a source of tension, and there have been several periods of violence in Northern Ireland since the partition.