From USA to Europe, through Ireland -

So many USA companies follow a common pattern when they want to start to compete in Europe: they basically do it starting their moves in Ireland.

The main reasons are :

English, as common language so they can communicate well each other and start with UK as main market target. In the main cities there are too many immigrants from other European countries, so to find native employees from Germany, France, Easter countries, Italy or Spain is not difficult. To build a service center offering a multi-language capabilities is not a big deal.
Low taxes offered by the government: this is one of the attractive aspects offered and very criticized by other European countries.
Competitive cost of living, which makes the investment to be lighter than in UK (specially London).
IT capabilities: there are a good bunch of companies already there, which attracts people with so many different skills.