The various alphabets in use in the modern world have complex histories. Their roots often come from purely pictorial (ideographic) systems of symbols, in which the picture directly represent objects. Over time some syllabic or phonetic symbols (in which the symbol stood for a sound) were added to the range of symbols, and it gradually became apparent that these were more flexible and useful as a basis for writing. An example of this evolution comes from Linear A and Linear B, two scripts used in the Mediterranean. Linear A was used by the Minoan civilization by about 2000 BC. It contained hundreds of signs, which were mainly ideographic, although some may have also represented phonetic sounds. Linear A is still undeciphered, but its descendant Linear B, which dates to five to ten centuries later, has been deciphered as a form of ancient Greek and contains just eighty-seven syllabic signs and one hundred ideographs. This is not as simple as a modern alphabet, but it is evidence of progress in that direction.
When it comes to the modern Western alphabet, the history is a tangled one. One possible chain of influence goes back to Egyptian hieroglyphs, which, by around 2650 BC, had been supplemented by twenty-two syllabic symbols used in combination with ideographs. One theory is that these symbols developed into an alphabetic system (known as the Proto-Sinaitic script) in the Middle East in about 1700 BC. This may have gradually changed into the Proto-Canaanite script, which in turn eventually mutated into the alphabetic Phoenician writing system. But this is all speculation, and the exact links are not known.
We do know for certain, however, that the Phoenician system was used widely around the Mediterranean area in about 1000 BC, that the Greek alphabet was a modification of it, and that the Romanized version of Greek became the basis of the Western alphabets used across most of Europe. So while the early part of the story is murky, we can trace the prehistory of our alphabet back at least to the Phoenician traders who spread it around the region, and possibly all the way back to Ancient Egypt.