The Word is: “because”
(The most common words in English.)
See video on how to use “because” here.
because
/bɪˈkɒz/
conjunction
conjunction: because
for the reason that; since.
“we did it because we felt it our duty”
synonyms: since, as, for the reason that, in view of the fact that, owing to the fact that, seeing that/as
“his classmates liked him because he was very friendly”
antonyms: despite
informal
used to introduce a word or phrase that stands for a clause expressing an explanation or reason.
“there’s probably somebody out there who would argue the point because Internet”
Source credit: Google