Although I would not consider myself conservative - at all - There is 1 instance that I can think of.

Abraham Lincoln and the Emancipation Proclamation. The freeing of slaves was in 1862 was done over the course of several months through various laws: the first laws forbade Union soldiers of returning fugitive slaves. Then Lincoln forced Congress' hand to compensate slave owners that freed their slaves. Finally the Emancipation Proclamation in late 1862, then the 13th Amendment the next year.

I know that a lot of people argue the reason why Lincoln did this, but that isn't the question here. I was just trying to show someone in the Republican party who, fought for and ultimately died for(Wilkes Booth claimed America was made for whites only) something he believed in.