How were the senators originally chosen? which amendment changed that?

For 125 years the Federal government adopted the way of electing senators stated in the constitution of 1788, which consists of electing senators by state legislatures. During the 1890s the House of Representatives passed several proposals of a new constitutional amendment for the direct election of senators, but it was until April 8th, 1913 that the 17th amendment was included for direct election of senators.  

to protest slavery i would think it would be a

nothing did. japan is wierd and always was.