Can't invade island even with Capital Ship (Destroyer)

[Red Ninja]

Playing as North Korea. Successfully isolated SK diplomatically and occupied the peninsula. Just one region is out of reach, an island south of the peninsula. I built 4 destroyers and positioned them directly next to the island. I put my land units in the region immediately across the straight. I don't see any SK navy and certainly not in the area.

I tried to "Attack" the remaining forces on the island. I tried to "Move" onto the island. All that happens is the "buh bum" sound. No message. No "Can't reach that region" or anything like that. Just a sound and they don't move. What's up? What's the deal with this? I hope SP3 has a better way to do overseas invasions bc SP2's is splotchy at best.

[Red Ninja]

Before posting this I thought I had read thru all the previous questions regarding this until I found one very old answer that cleared this up. For posterity's sake and anyone trying to find answers to this situation, I'll post here:

You have to eliminate country's entire navy that you are trying to invade EVEN IF their navy is on the other side of the planet. This is goofy AF, gamy and unrealistic but thems the breaks. I found out that SK's navy (44 patrol boats) was engaged in a battle with Japan in the Persian Gulf... yes... the Persian Gulf... IE the other side of the continent.

I watched as Japan manhandled the SK navy and once they lost all their ships I was able to cross the straight and occupy the last island.

[BosmangBeltalowda]

Thank you for writing down the answer here. I'm playing as Malaysia trying to invade China, but I can't land my unit despite my aircraft carrier and frigate positioned directly next to China. Search the entire web but found no answer. Decide to look at recent Steam discussion and found this. Turn out I need to eliminate China naval fleet in Syria and Somalia coast just to land my ground force at China.

Hopefully this mechanic doesn't carry over to SP3.