Please list some bad consequences of Columbus' voyage in 1492.

The most important negative consequences of Columbus's
voyage were the consequences that it had for the Native Americans.  They were hurt both
in the short term and in the long term by his "discovery" of the
Americas.

In the short term, the voyage (and the ones that
followed) caused various of the Indians to essentially become enslaved.  They were, for
example, forced to mine gold for the Spaniards.  This was certainly a major negative
consequence for them.

In the long term, things were worse
still.  With the coming of Columbus came epidemic diseases.  Europeans and other Old
World people had some immunity, but those of the New World had none.  These diseases
decimated the Native American populations as disease spread throughout the Americas. 
This was surely the worst consequence of Columbus' voyages.