Answer 1:
Religion.
Answer 2:
Hardly religion. The ideology of "Socialism/Communism"* has been used to justify more killings than any other belief system, or all the religious beliefs combined.
Hitler's National Socialist Germany - 15 million to 20 million.
Stalin's Union of Soviet Socialist Republics - 50 million to 100 million.
Mao's Communist China - 100 million plus.
Pol Pot's Commnist Cambodia - 3 million to 5 million.
Of course, any one inclined to socialism/communism could point out that those were not examples of "real" socialism/communism, which in their view is benevolent and just. But at the same time then, we would have to be fair and mention that any religious person is going to point out that the killings in the name of Christianity or Islam did not represent "real" Christianity or Islam, which in their view is benevolent and just.
The point is not then whether the given ideology was practiced in a "real" way, just whether there were people killed in its name.
Socialism/Communism had more people killed in its name than any other ideology, including all religions combined.
*Socialism and Communism are identical socioeconomic systems, the only difference being in how the goals are achieved politically. Socialism advocates a peaceful evolution into it, Communism a violent overthrow.
Racial idealism is the belief that certain races are inherently superior to others, based on characteristics such as intelligence, character, or physical attributes. This ideology has been used to justify discrimination, segregation, and violence against marginalized groups throughout history.
Well Ideology is a way of thinking. So the belief system of religions is their Ideology.
The belief behind honour killings, as found through online research, is that the victim has brought dishonour to the family. These acts are now referred to by some as gender apartheid.
religion
ideology
expansionists used the term "manifest destiny" to justify what belief?
At the core of free-labor ideology was the belief that individuals should have the freedom to sell their labor in a competitive market without coercion or exploitation. This ideology promoted the idea that hard work and skill should be rewarded with fair wages and opportunities for advancement, leading to economic prosperity and social mobility.
The concept of ideology has often carried negative associations because it can lead to close-mindedness, rigidity of thought, and belief in a singular truth that does not allow for alternative perspectives. Ideologies can be used to justify harmful beliefs and actions, leading to conflict, oppression, and division within society.
Ideology is a concept that makes up human life. Faith, belief, high drive and ambition are all sources of ideology that can be found in everyday life.
Social Darwinism
The belief is called the "Divine Right of Kings." This belief was used throughout the history of monarchy to provide the right of Kings not to be impeded by their subjects or court.
The belief that one race is better than others is known as racism. This belief can lead to discrimination, prejudice, and harm towards individuals based on their race or ethnicity. It is an unjust and harmful ideology that has been the root cause of many social injustices throughout history.