We analyze international co-authorship relations in the Social Science Citation Index 2011 using all citable items in the DVD-version of this index. Network statistics indicate four groups of nations: (i) an Asian-Pacific one to which all Anglo-Saxon nations (including the UK and Ireland) are attributed; (ii) a continental European one including also the Latin-American countries; (iii) the Scandinavian nations; and (iv) a community of African nations. Within the EU-28 (including Croatia), eleven of the EU-15 states have dominant positions. Collapsing the EU-28 into a single node leads to a bi-polar structure between the US and EU-28; China is part of the US-pole. We develop an information-theoretical test to distinguish whether international collaborations or domestic collaborations prevail; the results are mixed, but the international dimension is more important than the national one in the aggregated sets (this was found in both SSCI and SCI). In France, however, the national distribution is more important than the international one, while the reverse is true for most European nations in the core group (UK, Germany, the Netherlands, etc.). Decomposition of the USA in terms of states shows a similarly mixed result; more US states are domestically oriented in SSCI, whereas more internationally in SCI. The international networks have grown during the last decades in addition to the national ones, but not by replacing them.