They demanded (an) unconditional surrender.

他们要求无条件投降。

《牛津词典》

The enemy were forced to make an unconditional surrender.

他们试图以饥饿迫使敌人投降。

youdao

Even in case of an unconditional surrender, when the terms are dictated by the victor, they should nevertheless be embodied in a written capitulation as soon as practicable.

即使在 无条件 投降的情形，由胜方口述 投降条件时，亦应于最快时间内制作成书面文字。

youdao

Lee was sure Grant would not demand unconditional surrender.

VOA: special.2009.12.17

But he rejected General Shafter's demand of unconditional surrender.

VOA: special.2010.07.15

Grant demanded unconditional surrender.

VOA: special.2009.11.19

In 1945, the Allies rejected peace offers by German SS chief Heinrich Himmler, insisting on unconditional surrender.

CNN: Sunday,

The letter was given to General WHM Lowe after Pearse agreed to an unconditional surrender on 29 April, 1916.

BBC: Dublin may seek surrender letter

As U.S. strategists knew from having broken the Japanese military and diplomatic codes, there was virtually no inclination toward unconditional surrender.

FORBES: The Nuking Of Japan