The reason why U.S. Department of Defense started this is because the idea of Internet is to break up the packets in data and transmit as scattered, that way, hacker won't be able to get information in one packet. then when the transmission is complete at the end, the application put puzzles together and there is information.
You see, I posted this message, NONE of them will travel at same path! Say, maybe 500 parts of this goes to 500 different paths and arrived in AllDeaf server then that server put everything together, viola! complete message body.
very rare, everything goes at same path,
Also, other reasons involved is if one server got ka-boomed by enemies, the other end can always send back ask for missing data, so no data will be lost no matter what. That is purpose of thie Internet in the first place.
Also, the first Internet, there is NO graphic interface that you see here. Just line by line text, that is it! So Internet evolved during 80's and early 90s, around 1993 that is when Internet usage started to SKYROCKET big time.