Once regarded as a beacon of secularism in the Arab world, Tunisia has seen militant Islamists gain strength since the overthrow of long-serving ruler Zine al-Abidine Ben Ali in a popular uprising in 2011. The attack on the famous Bardo museum in the capital, Tunis, was the deadliest since the revolution, with at least 19 people - mostly European tourists - killed. No group has said it carried out the attack, but fingers are likely to point at hardline Salafi Muslim groups linked to either al-Qaeda or...