The United States is well-known for being extraordinarily late in abolishing slavery, and for denying black people basic civil liberties a mere three decades ago.
Now it is also well known for its tardiness in abolishing the death penalty. The death penalty has been abolished by the majority of the countries of the world, and by all Western industrial nations except for the United States.
The Council of Europe has called for the abolition of the death penalty. The United Nations called for moratorium in the US after it saw how the death penalty worked there, and the UN General Assembly has called for progressive abandonment of capital punishment for about a quarter-century. All major human rights associations want an end to the death penalty; the American Bar Association has called for a moratorium on executions; and various US medical associations have told their members that they should not debase their profession by helping with executions.
Many countries abolished the death penalty several decades ago, and some have constitutional prohibitions against it. A full list is available from Amnesty.