All the major gang syndicates are connected, especially when it comes to international borders, as they can help each other smuggle things in and out. So drugs are one of the major places that you see cooperation between the Irish and Italians still in Europe today. The more they can sell, the more money they make, so everyone's happy to help each other out.

In America, the Irish and Italian originated American gangs were often at ends with each other for control of territory, but since these groups were rarely united themselves they could easily convince one of the families to help them take out a rival so both sides benefited.