Here in this post above is clearly seen WHY the term Federal is the choice of some, and it is all about the POLITICS of today, not about impartial neutrality of historical discussion.
To many here, "Federal" is their new "politically correct" choice in discussion the army of the USA in 1861-65, for the political statement it makes about today, and it ties in directly and fully with the political landscape of 2010, and is meant to line up with the poster's modern political views right now.
"Federal" is political code, political red flagging done for modern reasons for modern readers. It is NOT used to be a neutral term. It is used as political short-hand, and another form of political correctness.
To insist the term Federal be used instead of Union is nothing but political, and it is specifically meant to be used to make specific political points about 2010. If that is not the intention of those who exclusively use Federal over Union, it is how it is being interpreted and accepted.
When you originally brought up this topic you said you avoided Union and chose Federal as a more neutral term. But then in your own follow-up post you yourself brought up the politics of 2010, revealing the true underlining motive.
This post above and all the "amen, brothers" that follow, (the message that "federal" carries today, is so clear and so obvious that no further comment is needed ! ... just an "amen" suffices) prove the exact point I was making in the first place: choosing Federal over Union, is not done for neutrality, it is done to underscore a modern political point, and to get the zealots excited. It is a charged term frought with modern meaning.