It was a war （the queen and her more prudent counselors wished to avoid（ if they could） and were determined （in any event） to postpone （as long as possible））.
1.看到括号了吧,从the queen到句子最后,都括起来,这是个定语从句,用来修饰前面的先行词war.
2.在这个定语从句内部,又有三个小的括号,一个是（ if they could）,这个在定语从句内部做条件状语从句,另一个是（in any event）,也表示条件,意思为“在任何情况下”,最后一个是（as long as possible）,意思是“只要有可能”.
3.去掉这些枝叶的东西,剩下定语从句的主干就是：主语是the queen and her more prudent counselors,谓语部分是wished to avoid and were determined to postpone.
最后,总的来说,这句话的意思就是,这是一场（女王和她的谋士们都希望在可能的情况下避免,并尽可能往后拖延的）战争.