What does it mean, a new form comes about only to replace an old form which has ceased to be aesthetically viable?

但是新的形式代替旧的形式,来换取审美的重生是什么意思？

耶鲁公开课 - 文学理论导论课程节选

He eventually switched; his New York this happened in many regiments in the Civil War it took so many casualties it ceased to exist and he switched to a Connecticut regiment and he served that Connecticut regiment through the summer of 1864.

他最终换了军队,内战期这很平常,他所在的纽约军队伤亡惨重,全军覆灭,他来到康乃狄格军队,他一直在此服役,度过了1865年夏

耶鲁公开课 - 美国内战与重建课程节选