▁' in vas ions ' ▁from ▁Upper ▁Peru ▁until ▁ 1 8 2 1 , ▁Bel gr ano ' s ▁campaign ▁is ▁widely ▁considered ▁the ▁decis ive ▁one . ▁ ▁Camp aign ▁to ▁Upper ▁Peru ▁By ▁June ▁ 1 8 1 3 ▁Bel gr ano ▁set ▁up ▁a ▁base ▁in ▁Pot os í ▁with ▁an ▁army ▁of ▁ 2 , 5 0 0 ▁men , ▁to ▁prepare ▁an ▁attack ▁on ▁Upper ▁Peru . ▁Go y ene che ▁moved ▁to ▁O ru ro ▁and ▁res igned , ▁being ▁replaced ▁by ▁Jo aqu ín ▁de ▁la ▁Pe z uela . ▁Bel gr ano ▁administr ated ▁the ▁zone ▁and ▁tried ▁to ▁revert ▁the ▁bad ▁impression ▁left ▁by ▁the ▁previous ▁campaign ▁of ▁Juan ▁José ▁Cast elli . ▁Bel gr ano ▁initi ated ▁good ▁relations ▁with ▁the ▁n atives ▁as ▁well . ▁Bel gr ano ' s ▁plan ▁was ▁to ▁attack ▁the ▁royal ists ▁from ▁the ▁front ▁and ▁the ▁sides , ▁with ▁the ▁aid ▁of ▁the ▁arm ies ▁of ▁C ár den as ▁and ▁Zel aya . ▁Both ▁arm ies ▁were ▁near ▁ 3 , 5 0 0 ▁men . ▁However , ▁the ▁royal ists ▁obtained ▁an ▁important ▁advantage ▁by ▁defe ating ▁C ár den as ▁and ▁getting ▁possession ▁of ▁his ▁papers , ▁which ▁gave ▁them ▁insight ▁into ▁the ▁patri otic ▁plans . ▁Bel gr ano ▁was ▁taken ▁by ▁surprise ▁at ▁Vil cap ug io ▁on ▁ 1 ▁October , ▁and ▁initially ▁gained ▁the ▁upper ▁hand ▁against ▁the ▁royal ist ▁troops , ▁who ▁started ▁to ▁fle e .