“Yamato” meaning/connotation

Hello,

I'm writing a fiction book and trying to use the oldest name for each country. I can make up one and if you have suggestions, great. I was going to use the country name "Yamato" as it seems the oldest. However, I've read it was used bit in WWII and may carry some meaning associated with imperialistic/militaristic things from that period. Could someone please tell me if this is a controversial term or if it is alright to use? Arigatō Gozaimashita.