What are negative and positive effects?

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

The battle of sabine pass is important because? a) it was a stalemate between union and confederate armies. b) it resulted in the largest confederate casualty in the war. c) it marks the failed attempt of the union army to invade the confederate state of texas. d) it was won by the union soldiers and marked a turning point in the western front of the war.

Search america's open door policy with china beginning in 1899. explain how relations with the united states and china have changed and the effects of the open door policy on both countries.