The state of Qin eventually swallowed up the six rival states.
Tips
usage
Strong negative connotation: implies seizing by force or absorbing greedily. Compare neutral 合并 ('to merge') and clinical 收购 ('to acquire'). 并吞 is the right choice when you want to portray the act as predatory.
memory
并 'combine' + 吞 'swallow' - picture combining things by literally swallowing them. Pure visual.
