You could use a lookahead:
re.split(r'[ ](?=[A-Z]+\b)', input)
This will split at every space that is followed by a string of upper-case letters which end in a word-boundary.
Note that the square brackets are only for readability and could as well be omitted.
If it is enough that the first letter of a word is upper case (so if you would want to split in front of Hello as well) it gets even easier:
re.split(r'[ ](?=[A-Z])', input)
Now this splits at every space followed by any upper-case letter.