unify, unite

合わせる(あわせる)	To unify. To bring different things together and make them fit. Like a band tuning up is called 音合わせ (making the notes fit). $$$

会わせる(あわせる)	To make two people meet each other. Not used.

併わせる(あわせる)	A formal word for unite. You don’t need this, either. NP