They have been a natural bridge from cash and checks to electronics. Historically, automated teller machine and debit card networks, much like the early check-clearing network in the US, were generally regionally based. Banks issued debit cards that could be used only on certain networks, which had limited reach across state lines.
Such crises can be the result of the breakdown of infrastructure that assures essential linkages between financial institutions. They could spread through a succession of defaults or because a large number of financial market participants all want to liquidate certain positions simultaneously.