In which key these chords go?

In which key these chords go?

I was recently playing my guitar, suddenly I found that C, D and E chords sound good together in a progression, but I was not able to find a key in which these chords go together, so I wondered what is going on Like while writing music is it necessary to first pick a key and then start playing

The progression C, D, E is not tonalic, which means it doesnt have a tonic key. Its just major chords in parallel. You can use them to create an effect or a feeling, or even combine them in A-Tonic music music without a classical key. Alternatively, you can use it inside a Tonalic progression to create modulation change for scale examples: Modulation from C to E Through Tonics C G C to accomplish a C key and than - D E - to transpose to E scale and than B E to accomplish this new Tonic https:clyp.itvqnn21qd Modulation from Fm to Am Through Dominants Same idea: but I use C and G as dominants: Am C Am C D E Am E Am https:clyp.ittevvxw0u A-Tonalic Example This one is not really good because I dont know much about A-Tonalic music, but you can get the idea https:clyp.itengzhjcp Im sorry the examples are on piano, because Im not a guitarist, but the music theory is the same :