In the sentence "that organization was founded in 1978 when the natural disasters had increased..."
Use {{
Citation needed}} if you are simply requesting a source that says that the organization was founded in 1978
Use {{
Chronology citation needed}} if what you are requesting is a source that says when the disasters increased in relation with the year of foundation
In the sentence "those Celtic tribes survived more than one invasion...":
Use {{
Citation needed}} if you are simply requesting a source that says that those tribes survived many invasions