An earlier publication (Grossetti et al., 2014) has established that we are attending a decreasing concentration of scientific activities within " world-cities ". Given that more and more cities and countries are contributing to the world production of knowledge, this article analyses the evolution of the world collaboration network both at the domestic and international levels during the 2000s. Using data from the Science Citation Index Expanded, scientific authors' addresses are geo-localized and grouped by urban areas. Our data suggests that interurban collaborations within countries increased together with international linkages. In most countries, domestic collaborations increased faster than international collaborations. Even among the top collaborating cities, sometimes referred to as " world cities " , the share of domestic collaborations has gained momentum. Our results suggest that, contrary to common beliefs about the globalization process, national systems of research have been strengthening during the 2000s.