How to get the Maven project window in Intellij 14 | Update: cannot see the right side "tab bar" with Maven project
I had similar problem until I right-clicked the option in POM "Add as Maven Project".
Notice: IDEA 2019.2 and I couldn't even find Maven in "Tool Windows" of the (existing) project before it.
First, make sure you have enabled maven plugin in
File → Settings → Plugins → Maven Integration
If so and still the tool window is hidden then
go to View → Tool Windows → Maven Projects to open it.
For those stuck with this issue, enable View -> Tool Buttons.