Whakaotihia te rerenga e whai ake nei: I te marama o Mei 1846, ka whakarere a Buckner i tana tūranga whakaako ki te whawhai i te Pakanga o Mexico-American, ka uru ki te 6th U.S. Infantry Regiment. Ko ana mahi tuatahi ko te kohi hoia me te kawe mai ki te rohe o Texas. I te marama o Noema 1846, i whakahaua ia kia uru atu ki tana kamupene i te mara; i tutaki ia ki a raatau i te huarahi i waenga o Monclova me Parras. I uru te kamupene ki a John E. Wool i Saltillo. I te marama o Hanuere 1847, i whakahaua a Buckner ki Vera Cruz me te wehenga a William J. Worth. I te wā ko te Maj. Gen. Winfield Scott
I te whakaekenga o Vera Cruz, ka whakaekea e te roopu a Buckner etahi mano o nga hoia eke hoiho Mexico i tetahi taone tata e kiia ana ko Amazoque.