Okay, so Rebekah TJLC Explained has suggested that most of the stuff Mycroft is involved is in Asia, but I think, not all. He "wades in" to Serbia, and he obviously involves himself with Magnussen, who is European, has well as issues of "national" importance, like the Bruce-Partington plans. Perhaps he is simply involved in issues of surveillance and "secret states"?
35 Best Sherlock Quotes from 'The Lying Detective' (4x02
Quote from Sherlock 4x02 │ Faith Smith: Well, we just came that way. Sherlock Holmes: I know, it’s a plan. Faith Smith: What plan? (people tracking Sherlock – laughing) Mycroft Holmes: What is it? What… What now? One of the Mycroft’s minions: Sorry, um, traced his route on the map. (route makes the phrase “fuck off”)