Sentence Correction

Hi All,

In the below question of OG-11 Q51. OA is [spoiler]"D"[/spoiler]. OG says that "in that" is not used anymore. Due to that reason option "A" is wrong. The option [spoiler]"D"[/spoiler] is correct since it contains "For" which means
"because" here.

But somewhere I read that "in that" is better choice than "because". Can someone please help me understand is "in that" a better option or is simply incorrect ?

============================================

The Olympic Games helped to keep peace among the pugnacious states of the Greek world in that a sacred truce was proclaimed during the festival’s month.
(A) world in that a sacred truce was proclaimed during the festival’s month
(B) world, proclaiming a sacred truce during the festival’s month
(C) world when they proclaimed a sacred truce for the festival month
(D) world, for a sacred truce was proclaimed during the month of the festival
(E) world by proclamation of a sacred truce that was for the month of the festival

Regards
Mohit