I've been doing some research into the Gods that were worshipped in the area that I live in and I come across several Gods that have the same name but are different and are somewhat intermixed with other Gods.
I'm confused...

An altarstone for Mars Halamardus was found near the town where I live. When I research him I find a reference in the Encyclopedia of Norse and Germanic Myth Folklore and Magic that states that oftentimes Mars can be seen as a Roman interpretation of Tyr, like Mars Thingsus. But Mars Halamardus is most likely not?

How can you have multiple gods called Mars, that are somehow related to Tyr, but not all. Are these different Mars' all different Gods, or representations of the Mars we know from the Roman pantheon?

How I look at it now is that Romans invaded Europe and brought with them their gods. And when people try to intermingle they look for similarities, right? The Roman and Germanic Gods Tyr and Mars were kind of similar. So one God blends into the other. But maybe not always? And not always the same or in the same measure? Is Mars Halamardus a pure Roman God?

Sorry for the rambling.
Anybody care to help me shed some light on this?