▁have ▁agreed ▁to ▁conce al ▁the ▁treat y ' s ▁existence ▁or ▁subst ance ▁from ▁other ▁states ▁and ▁the ▁public . ▁Such ▁a ▁commit ment ▁to ▁keep ▁the ▁agreement ▁secret ▁may ▁be ▁contained ▁in ▁the ▁instrument ▁itself ▁or ▁in ▁a ▁separate ▁agreement . ▁ ▁According ▁to ▁one ▁compilation ▁of ▁secret ▁treat ies ▁published ▁in ▁ 2 0 0 4 , ▁there ▁have ▁been ▁ 5 9 3 ▁secret ▁treat ies ▁negoti ated ▁by ▁ 1 1 0 ▁countries ▁and ▁independent ▁political ▁entities ▁since ▁the ▁year ▁ 1 5 2 1 . ▁Secret ▁treat ies ▁were ▁highly ▁important ▁in ▁the ▁balance - of - power ▁diplom acy ▁of ▁ 1 8 th ▁and ▁ 1 9 th ▁Europe , ▁but ▁are ▁rare ▁today . ▁ ▁History ▁The ▁" el abor ate ▁al liance ▁systems " ▁among ▁European ▁powers , ▁" each ▁secured ▁by ▁a ▁network ▁of ▁secret ▁treat ies , ▁financial ▁arrang ements , ▁and ▁' mil it ary ▁understand ings '" ▁are ▁commonly ▁c ited ▁as ▁one ▁of ▁the ▁causes ▁of ▁World ▁War ▁I . ▁For ▁example , ▁the ▁Re ins urance ▁Tre aty ▁of ▁June ▁ 1 8 8 7 ▁between ▁the ▁German ▁Empire ▁and ▁the ▁Russian ▁Empire ▁( neg oti ated ▁by ▁German ▁Chan cell or ▁Otto ▁von ▁B ism ar ck ▁in ▁order ▁for ▁Germany ▁to ▁avoid ▁a ▁two - front ▁war ), ▁was ▁a ▁" high ly ▁secret ▁treat y " ▁in ▁which ▁the ▁two ▁powers ▁p led ged ▁a ▁three - year ▁period ▁to ▁remain ▁neutral ▁should ▁the