(For younger readers, that Oldsmobile reference in the title recalls an auto industry sales pitch to younger drivers who had categorized Oldsmobiles as an older person's car. Since Oldsmobiles no longer exist I guess the ad campaign had limited success.)
The earliest written references to Chianti date to the thirteenth century. In the mid-eighteenth century the wine was codified by Baron Ricosoli to be a red wine blend of 70% Sangiovese, 15% Canaiolo, and 15% Malvasia and that's the way things were for well over a hundred years. The twentieth century became an evolving proving ground for Chianti as those blending proportions gradually changed with Sangiovese increasing its presence in the blend and the white Malvasia decreasing until today most Chianti is a single-varietal Sangiovese.
Or...it may be a blend of four dozen grapes! Leave it to the Italians to change their wine industry laws from already-confusing to even more so! Legally, today Chianti must be at least eighty percent Sangiovese with Canaiolo being the secondary varietal with five percent of the blend being reserved for "other" grapes. Up to four dozen! But no white grapes are allowed anymore.
To understand this evolution we have to go back to the late nineteenth century when the Phylloxera epidemic basically destroyed all vineyards in Italy. With the industry in shambles, emigration ensued with vineyard workers and winemakers moving to new world environs around the world. As the Italian wine industry re-planted with a lower labor force, it was the higher yielding Sangiovese clones that they chose to use. Basically, mass marketing had come to Italy and the Chianti our World War II GI's came to love over there was that lighter, simpler variety of wine.
So when those guys returned home after the war that was the wine they wanted and in 1967 when Italy created its DOC standards for Chianti, that was what was codified. That standard stood for a mere fifteen years though before Tuscan winemakers could tolerate the mediocrity no longer and defying convention, threw the rule book out the window and made world class wine with Bordeaux grapes integrated into the mix. These "Super Tuscan" wines forced the bureaucrats to amend rules that no longer made sense. Not only would the new Super Tuscans be written into the appellation system (Reserve Chianti?) but Chianti, itself, would be improved.
Through it all, whatever style of Chianti has been presented to the American consumer, the wine has continued to be the most popular import on our store shelves.