One guy with a machine gun could conquer this country in 10 minutes. And if it's truly sovereign then it would be completely legal.
What is "non" Agressive war is always defined by who holds the biggest gun.
In August of 1978, a number of Dutch men came to Sealand in the employ of a German businessman. They were there to discuss business dealings with Sealand. While Roy was away in Britain, these men kidnapped Prince Roy's son Michael, and took Sealand by force. Soon after, Roy recaptured the island with a group of his own men and held the attackers as prisoners of war.