Alliance - When Dwarves first migrated to Beleriand, they came in contact with the Elves who had been living there for some time.  After a period of adjustment, the two races became amicable.

 

"It came to pass during the second age of the captivity of Melkor that Dwarves came over the Blue Mountains of Ered Luin into Beleriand.  Themselves they named Khazâd, but the Sindar called them Naugrim, the Stunted People, and Gonnhirrim, Masters of Stone...the Naugrim came forth into Beleriand; and the Elves were filled with amazement, for they had believed themselves to be the only living things in Middle-earth that spoke with words or wrought with hands." ~The Silmarillion, chap. 10 (Of the Sindar)

 

When Morgoth returned to Angband and tried to take Beleriand, the Dwarves joined the Elves.

 

"Therefore Thingol took thought for arms, which before his people had not needed, and these at first the Naugrim smithied for him; for they were greatly skilled in such work...A warlike race of old were all the Naugrim, and they would fight fiercely against whomsoever aggrieved them: servents of Melkor (in this case Orcs)..." ~The Silmarillion, chap. 10 (Of the Sindar)