Can I Install an Win XP OS on my new External Drive?

I have a " Back UP " CPU Running Windows 7. I bought an external Drive to possibly install An older Windows “XP” OS. I want to do this so that I can play my older “Video Games” that will not run on the newer Window OS’s.

I just bought a Copy of Windows “XP” w/ the product key to install on an older " Back Up " CPU that I want to use to ONLY run my older “Video Games” on. I have another newer CPU running Windows 10 that I will use for everything else. This “Back Up” computer will be used exclusively to play my older “Video Games” & will not need internet access although I can enable this “Back Up” CPU to have Internet Access if needed.

This back up CPU is running Windows 7 Professional & is blocking me from installing this Windows “XP” OS because i’m trying to install an older Windows OS than is currently installed on my CPU

I sure would appreciate any & all comments.

I don’t believe the drive is bootable.

Thank you Joe