Emperor Haile Selassie of Ethiopia did not modernise his military with false sense that diplomacy, ie the participation of Ethiopiaas a founding members to League of Nations guaranteed his country from being invaded. He was proven wrong when Bennito Mussolini's Italy invaded Ethiopia.
He was wrong again when the Leagues of Nations did not raise a finger.
He was wrong again when the United States had a Marine officer with an observer status witnessing the Italian invasion.
So to was Poland. They believed that their military treaty with United Kingdom would protect them from German invasion.
They were wrong. The Germans invaded.
They thought the British would send military reinforcement. They were wrong. The British retreated to the beach of Dunkirk and beyond.