Many inventors seemed to have protected their inventions worldwide, prior to the introduction of the PCT application. For example, Alexander Graham Bell. How did these individual inventors protect their inventions in the US and Europe with filing patent applications one-by-one all around the world?
Patents has been around for a long time .
Patents for international purposes has only really gained importance with the raise in efficient global trade and even then for most purposes it is sufficient to have a US patent as that will block transgressions of copying an invention and export it into the US market which historically have been the largest and most important market for any international companies.
So sure, somebody may have copied an Graham Bell invention in some local market but it didn't really matter unless that Graham Bell intended to explore that overseas market, which were unlikely as there were too little money to be made in most overseas markets compared to the US.