Unlike the Mardonalians, and the villains generally in the series, the Kondalians are not Absolute Xenophobes, but willing to co-operate peacefully with other planets. That said, they are typically portrayed as a species of Proud Warrior Race Guys, with a strong whiff of Barsoom. They're very flawed good guys, and they do occasionally get called out on their warmongering by the human protagonists.
Older Than They Think: A "dark star", essentially a black hole, and mushroom clouds produced by the atomic/total conversion of explosive shells. Both in The Skylark of Space, published in 1928.
Early drafts are said to go all the way back to 1916. That is sixty years before Star Wars.