C++ has had excellent support for concurrent programming ever since the C++ 11 language standard came out. Until then, threading was an affair that was handled by platform-specific libraries. The Microsoft Corporation had its own threading libraries, and other platforms (GNU Linux/macOS X) supported the POSIX threading model. A threading mechanism as part of the language has helped C++ programmers write portable code that runs on multiple platforms.
The original C++ standard was published in 1998, and the language design committee firmly believed that threading, filesystems, GUI libraries, and so on are better left to the platform-specific libraries. Herb Sutter published an influential article in the Dr. Dobbs Journal titled, The Free Lunch Is Over, where he advocated programming techniques to exploit multiple cores available...