《战国策·楚一·张仪为秦破从连横》
至于秦国之所以十五年不出兵函谷关来攻打诸侯，是因为它有吞并诸侯统一天下的野心。
 且夫秦之所以不出甲尉函谷关十五年以攻诸侯者，阴谋有吞天下之心也。
As for the reason why Qin did not send troops out of Hangu Pass to attack the states for fifteen years, it is because it has the ambition to annex the states and unify the world.