Look at the Album name and Artist name... If they are slightly different, iTunes will see them as 2 separate things.
Spot on, and you can see the different name in the album listing.
You can manually edit this:
Go into music and select List View (view Menu), sort by Artist name (click the 'Artist tab) and then scroll down to 'City and Colour'. You should see two different names, one being just 'City and Colour' and the other 'City and Colour Fxxxxx' as seen in your screen cap.
Right click on the ones that you want to change and select 'Get Info'. Click on the Info tab, and you can now manually edit the Artist Name, Album Name, in fact any of its attributes.
You can batch edit by making a multiple track selection and then editting as above, but there are minor complications with this, and if you haven't done it before, it's best to try one track at a time.
Once you've edited all the tracks they should now appear in the same album.
It's important to do this in List View, because if you choose Album View and make a typo, the track will move from the Album that you're working on and you will have to hunt for it.
It's something that happens quite often in compilation albums when the producers haven't written the metadata properly.
