The and the were relative tribes to the sioux

What would lead a historian to consider two events to have a relationship of correlation rather than causation?

    which of the following was anecological  result of european exploration from 1400 to 1800?   a.  increased trade with east asia      b.  the spread of epidemic diseases      c.  expansion of english territory      d.  the spread of christianity

Controlled eastern europe a: communist countries b: democratic countries