Are you able to post the excel file?
Montana isn't showing up because Tableau doesn't know what country your data is in. There is also a Montana in Bulgaria.
Make sure you have a country column in your data, make sure it's Geographic Role is set to Country, and make sure it is in your view (Level of Detail shelf is fine).
That you have to do this hadn't occurred to me before. Another way to force this without changing the source would be to include: "USA" as [Country] as custom SQL
You could also create a calculated field to calculate the country from the state for your data.
Maryland has the same problem. There is also one in Uruguay. Any time I hear a question about Montana or Maryland, I know that's the problem. We've discussed how to make this more automatic in a future version of Tableau.
assigning the country definitely worked. I would have never thought of other countries. I map north american on the same map often (U.S. & Canada) i will select none instead of the U.S. defalt. anything that would be automatic will be great