The message is:
I wrote this using Roman numerals only.
The rearanged parts of the rebus are:
I — an eye
WROTE — a writing hand
THIS — a pointing hand
US — United States
IN — India
G — 9.81 (m/s², Earth's gravity)
· · ·
ONE — number one
minus E — −2.72 (an approximation of −e)
LY — Libya
That accounts for most of the message, but there's a gap in the middle
The gap in the middle ...
... can be filled by observing which letters were chosen as hints in the pattern for the sentence. They are I, L and M, which are all roman numbers. All other letters in the sentece aren't Roman numbers; they are represented by a dash. (That also means that the second word is "wrote", not "write".)
The expression ROMAN NUMERALS fits the given pattern ••M•• ••M•••L•.
As fot the title:
Roman numerals were used by a large number of people. (We even still use them today in some contexts.) And there's the big hint "number" right there.