Soda bread is a soft textured cake like bread that rises due to the reaction of the acid of a liquid like buttermilk, and a base like baking soda. ,
Although the Irish didn't invent Soda Bread it is most often identified with them. The "soft wheat" is the only suitable flour that can grow in Ireland's climate, and when mixed like a traditional dough it doesn't form any gluten like a traditional yeast bread, it does work well with a soda bread recipe.The Idea of using soda to leaven bread was done by the American Indians centuries ago, where they used pearl-ash or Potash( a natural soda in wood ashes) ) in their breads to make them rise.
The cross on the soda bread has several explanations, Legend has it that folks did it to "let the devil out" while it's baking for good luck, and others say that it made it easy to divide into 4 pieces. It was also a symbol for a cross during Christian holidays.
One of the earliest recorded publications of soda bread was in 1916. The editor of "The Gentleman's Magazine" in England was challenged to come up with a way to use poor soft wheat to make a bread.
He tried several experiments with his baker and came up with a bread using half wheat and half mashed up potato and soda ash instead of the usual yeast leavening.
Soda Bread and the Potato Famine of 1845
In September of 1845 a blight hit the potato crops of the Irish people who was very dependent on potato for food. A poor country discovered that potatoes and milk made a nutritious enough meal to exist on and you could grow more potatoes per acre than any other crop. Soda bread was probably not made as much because of this reason.
While some say that soda bread was invented during the great potato famine this is not true. It did start to become popular in Ireland at this time so the famine, surely, spurred it's popularity.