Speaking after a visit to the country's national cemetery, South Korea's first female leader pledged to spread wealth more evenly.
Ms Park, 60, said she will hold talks with North Korea on resuming aid, but only if it abandons its nuclear weapons programme.
The impoverished North launched a rocket last week that critics said was a test for technology that could one day be used to build a long-range missile carrying a nuclear warhead.
"North Korea's missile launch showed how grave the security reality is that we are faced with," Ms Park said.
She will take office in February and signalled she would continue outgoing Lee Myung-bak's tough line on territorial claims that Japan has on South Korea.
The relationship between them, both close allies of the West, has been damaged by an island row and the issue of an apology and compensation from Japan for the forced sexual slavery of Korean women in the Second World War.