MySQL Foreign Key Error: Can't create table, MySQL

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drop table if exists history;
drop table if exists class_members;

CREATE TABLE `class_members` (
  `id` int(11) NOT NULL,
  `username` varchar(65) NOT NULL DEFAULT '',
  `password` varchar(65) NOT NULL DEFAULT '',
  `email` varchar(65) NOT NULL,
  `mod_timestamp` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  PRIMARY KEY (`id`),
  UNIQUE KEY `username_UNIQUE` (`username`),
  UNIQUE KEY `id_UNIQUE` (`id`),
  UNIQUE KEY `email_UNIQUE` (`email`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 
;

CREATE TABLE `History` ( 
   `history_id` INT(11) NOT NULL AUTO_INCREMENT, 
   `username` VARCHAR(65) NOT NULL DEFAULT '', 
   `timestamp` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP, 
   `ip` VARCHAR(20) NOT NULL,  
   PRIMARY KEY (`history_id`), 
   CONSTRAINT `fk_history_member` FOREIGN KEY (`username`) 
   REFERENCES `class_members` (`username`) 
   ON UPDATE CASCADE);

insert into class_members (id, username, password, email) values (1, 'abc', 'abc', 'abc');
insert into history (username, ip) values ('abc', '1.2.3.4');
select * from history;


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