Unfortunately, the wicked awesome mysterious history of the Plain of Jars is intertwined with the horrifying history of the Secret War in Laos. Other tourist areas have a lot of evidence of the war (one of the ceremonial bells at the Elephant Cave in Vang Vieng is made out of an old bomb shell) but Phonsavan is famous for two things: jars and bombs. There are a couple of UXO information centers in town with more information about the effort to clear mines.
Before entering the Plain of Jars sites, there are signs indicating, basically, to stay on the trails to avoid being blown to smithereens. Good advice.
Many of the jars are damaged by bombs and there are bomb craters labeled alongside the jars. The Lao army used this cave (next to Jars site 1) during the Secret War.
The standard tourist circuit in town also includes a visit to an old Russian tank left rusting in the forest, and the tourist information center itself greets visitors with this: