The DUP, the story so far:

Formed to give Northern Irish Protestants even more control, driving Catholics out and end UUP cooperation with the Republic.

Result: the conflict it helped cause resulted in direct rule from Westminster, drove many Protestants to emigrate and... https://twitter.com/squinteratn/status/1336308917614342147

... led to the GFA, giving the Republic a say in NI's affairs.

Then...
DUP force changes in the GFA (St Andrews Agreement) because dissatisfied with its inability to control Stormont post agreement.

Result: deadlock in Stormont, leading to more direct rule, this time with...

... input from the Republic, as well.

In 2016, DUP support Brexit with Mysterious Money to keep the EU out of NI.

Result: EU to open office in NI, with special input into NI's affairs under a separate treaty.

One might legitimately wonder which side the DUP are really on.