Ancient Egyptians used rings of grass and other short-lived materials to symbolize eternity. They placed these rings on the bride and gooms’ left hands, on any finger, because they thought a vein ran from the left hand to the heart. In this way they believed the bride and grooms’ hearts were literally linked to each other and to eternity.
Europeans used a coin, broken by the groom at engagement and rejoined at the wedding. He would go, e.g. to war, and keep half the coin. The other half was the bride’s engagement token.
Soon rings replaced coins as they were easier to break and easier to display. The bride-to-be and her intended strung the ring pieces on strings arond their necks. The rings were often engraved with sayings about love and fidelity andso on.
Rennaissance Italians invented the diamond engagement token. Diamonds were a symbol of love to them. In the 15th or 16th Century one Italian noblewoman wore a diamond engaement ring. It caught on eventually.
Brides didn’t wear white until the 1830’s, when it slowly started becoming popular after Queen Victoria wore white at her wedding. Before that, white was considered a funeral color in Europe and the USA. Brides wore their favorite dresses of any color, but the most preferred bridal colors were purple for queens, crimson and royal blue in some cases, and often green for ordinary women. Asian women mostly wore red and gold, their “lucky” colors. They considered white and black bad luck.