It is easier and more commonplace for companies and corporations to merge together - but it is rare for churches to do so.
Every few blocks in America, you can see a church building. Why so many? Did God call all of them to start churches? I dont think so. When He does, it is usually among unreached peoples.
These churches on every block are usually branch offices of a head office, that compete with other head offices.
Is it clashing egos and flesh that prevent more mergers especially when doctrines are similar?
Here is a juwo on when our church merged with another.
http://juwo.com/nodepad/demos/thoughts/churches_merging.html