Mera agreed with the arranged marriage between King Arthur and Princess Diana of Themyscira. As long as it brought piece, she was willing to be part of the lie.
But after Queen Hippolyta's murder, the atlanteans were blamed. Peace was over. Arthur and Mera married instead.
Before things got worse, Mera decided to take matters into her own hands; encouraged by Orm, her brother in law, Mera left Atlantis to confront Diana.
This was a trap set by Orm and Penthelisea, Diana's aunt. The Queens of Atlantis and Themyscira fell for it and engaged in mortal combat.
Mera used her hard-water powers to fight Diana.
All in the name of peace and her love Arthur.
She was ready to kill or die.
Sadly, the savage Diana was swifter than Mercury.
And the Queen of Atlantis was beheaded.
Mera's death led to the sinking of Europe.
And eventually, the end of the world!