As for why the second summit in Hanoi might have fallen apart.... Seoul's foreign ministry thinks the problem was on the differing expectations for the North's denuclearization.
Our Lee Ji-won tells us more.
South Korea's foreign ministry has pointed to the different ranges of denuclearization North Korea and the U.S. brought to the table as the reason for the collapse of the Hanoi summit last month.

During a meeting on Monday of parliament's foreign affairs and unification committee, Minister Kang Kyung-wha said the U.S. wanted to draw a big picture of denuclearization and its corresponding measures, but that the North was only prepared to discuss its Yeongbyeon nuclear facility.

The ministry later added that Washington focused on defining denuclearization, freezing weapons of mass destruction and missile programs and developing an overall roadmap, while the North focused only on the denuclearization steps that can be taken at the moment.

On sanctions alleviation, Kang said the North will need to take bolder steps towards dismantling its nuclear program.

To a lawmaker's question on whether the U.S. doesn't consider sanctions alleviation as part of its corresponding measures, Minister Kang said she does not think that's the case,... hinting at the possibility of a partial lift depending on the North's moves.

In solving the current tug of war, the minister said South Korea must open all possibilities, including sending a special envoy to the North, and possibly having another inter-Korean summit.

On the latest activities at the Dongchang-ri missile site, Seoul's unification minister Cho Myoung-gyon said there is a possibility that such restoration activity could have been to show the actual blowing up of the site, if the two sides had reached a deal in Hanoi.
But with activities continuing there even after the summit, Cho said there is a need to continue watching and analyzing the North's intentions.

When asked if the North is still willing to give up its nuclear weapons, Minister Cho said North Korean leader Kim Jong-un is focused on developing its economy,... and that its thought Kim would need to denuclearize his regime to achieve that and obtain a security guarantee.
Lee Ji-won, Arirang News.