IntelliJ has different process to build war:
Goto -> Files -> Project Structure -> Artifacts
In artifacts tab, you will see a small + button on top right corner.
Click it and fill up the right panel data such as name and output directory.
Make sure to create the Manifest file. Keep default location for Manifest file.
After building manifest, click apply->Ok.
Now you can go to Build-> Build Artifact.
Your .war file will be ready in the output folder you specified above.
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