Global.asax is only present when there is a reason to hook into it. The default MVC6 project has no hooks into it, therefore it doesn't provide one. Just add new item, global.asax
I should also suggest, that I would avoid creating a global.asax unless you need absolutely need it. People tend to reach for Application_Start or Session_Start first when there are probably better places to do what you need to do. Consider creating an OWIN module, or consider adding your own Startup module.
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