In the 21st century, with the prevalence of air travel, global near-instantaneous communications, and active cultures of well-financed scientific research on several continents, you would think that the physics enterprise would be thoroughly homogenized, at least across places with similar levels of resources. Sure, really expensive endeavors would be localized to a few places (e.g., CERN), but the comparatively cheap subfields like condensed matter physics would be rather uniformly spread out.
Strangely, in my (anecdotal, by necessity) experience, that doesn't seem to be the case. One area of my research, looking at electronic/optical/thermal properties of atomic and molecular-scale junctions, has a very small number of experimental practitioners in the US (I can think of a handful), though there are several more groups in Europe and Asia. Similarly, the relevant theory community for this work, with a few notable exceptions, is largely in Europe. This imbalance has become clear in terms of both who I talk with about this work, and where I'm asked to speak. Interestingly, there are also strong regional tendencies in some of the citation patterns (e.g., European theorists tend to cite European experimentalists), and I'm told this is true in other areas of physics (and presumably chemistry and biology). I'm sure this has a lot to do with proximity and familiarity - it's much more likely for me to see talks by geographically proximal people, even if it's equally easy for me to read papers from people all over the world.
Basically, physics areas of pursuit have a (surprising to me) large amount of regional specialization. There's been a major emphasis historically on new materials growth and discovery in, e.g., Germany, China, and Japan compared to the US (though this is being rectified, in part thanks to reports like this one). Atomic physics w/ cold atoms has historically been dominated by the US and Europe. I'm sure some of these trends are the result of funding decisions by governments. Others are due to the effect of particularly influential, talented individuals that end up having long-lasting effects because the natural timescale for change at universities is measured in decades. It will be interesting to see whether these inhomogeneities smooth out or persist over the long term.