Cadence & the Key

Hi Everyone I was wondering if hearing a perfect cadence could help determine the key of a piece of music.

My friends & I, we are trying to put a band together, came up with a chord progression (found below) and i was wondering what the key of this was in. *currently i am the one most interested in music theory and how to apply to music making - i play guitar*

Dmin - Gmaj - Cmaj - Cmaj9 - Amin (repeat)

Note - all of these are played within the first 3 frets, which i believe is the first position *i maybe wrong - please correct me if i am*

I am thinking that the Amin is the key of the progression because the Cmaj9 seems to have an "Authentic Cadence" right to the Amin.

Please let me know what you think & please be as honest about my thoughts as possible because i am very very interested in understanding musical theory and applying it to my (and our) practice.

Thank you,

You're in D Dorian. Read up on Keys and Modes. It will explain it there.

My question still kinda stands.... "if there is cadence in a chord progression is it save to say that the "ending" or "starting" chord is the key of that song/progression"?

Usually this is the first thing you look for. Some progressions change through modes multiple times before you return back home... where ever that is. The key of a song or progression depends on the entire journey, not just the start or end. Though, the starting/ending point is a good indicator of what mode you're in.

Gotcha!! thanks Jeff!

Right now i think that all of the mode information is alil much for me but i do have a basic understanding of how they supposed to work in theory.