Two independent clauses can be joined by a colon to make one compound sentence if the second clause expands on or explains the first clause. Here are some examples:
Fascists have a problem: Donald Trump is a Republican.
Terrible body odor is useful: it makes room for your bags on the seat next to you.
Banal thoughts are like fish: they swim in a sea of words.
Love is magic: it makes warts disappear.
Writing gibberish has an upside: typos are never an issue.
Back pain and good writing are similar: sometimes they require surgery.
Gun violence is an American mushroom: it keeps popping up and it’s poisonous.
Alternative medicine is like alternative arithmetic: it doesn’t add up.