They were tolerated as a fake opposition until the inevitable time came when national politics got too serious for them. They merely got in the way of serious discussion until the split between North and South became too serious to be settled in the realm of politics. Any serious issue would break the modern Republican Party. America needs a post-Cold War political party. Democrats want American armed forces all over the world enforcing their agenda.
Republicans are happy with that.
All they want is a bigger military. What it is used for is of no importance. They just want more troops and more dollars for the Defense Department. They are still a Cold War party. Democratic trade policy is aimed at pushing a liberal agenda.