O que significa 仏教的な無常観に基づきながらへいけいちもんおえいがとせいすいのれきしをかいています。 ?

See a translation

I tried translating by using an online dictionary as follows.
(Please be aware that I'm not an expert in this field so there may be any mistakes in it in wording, but I think you can roughly get the point...)

"This writes the history of the prosperity and downfall of the Taira family (Heike) based on Mujokan (Buddhist concept of the impermanence of worldly things) in Buddhism."

I found out a typo error (お -> の) in the sentence you wrote. I think the correct sentence should be "仏教的な無常観に基づきながらへいけいちもん'の'えいがとせいすいのれきしをかいています。 (仏教的な無常観に基づきながら平家一門の栄華と盛衰の歴史を書いています。) ," right?

Hope this would help you