Why do most flags have red in them?

Related questions

1. Why is the Dutch flag not orange?
2. Which flag has the most colors?
3. Why do the Dutch wear wooden shoes?
4. Why do the Dutch wear orange on St Patrick's Day?
5. Why do Germany wear green?
6. Why is Liberia's flag similar to the American flag?
7. What is the main religion in Singapore?
8. Why are carrots orange now?
9. Is Malta a good country to work?
10. Why is there no orange in the Dutch Flag?

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2. #scientific
3. #reason
4. #hardiness
5. #probably
6. #faced
7. #believe
8. #flags
9. #having
10. #nation
11. #valor
12. #contain
13. #revolution
14. #sacrifice
15. #represents
16. #depicts
17. #courage
18. #national
19. #there
20. #because
21. #hardships
22. #colors
23. #color
24. #blood