Final answer:
Coastal defense is the element that enables a sea-dependent nation to protect its political, economic, and military strengths seaward.
Step-by-step explanation:
In the field of maritime security or naval strategy, the element that enables a sea-dependent nation to protect its political, economic, and military strengths seaward is known as coastal defense. Coastal defense involves protecting the coastal areas and waters of a nation from potential threats. It can include the deployment of military forces, the establishment of naval bases, and the use of surveillance and intelligence-gathering systems to detect and respond to maritime threats.
For example, a sea-dependent nation may build naval bases and patrol its coastal waters to deter and defend against potential attacks from other nations. These coastal defense measures help protect the nation's political, economic, and military interests by ensuring the security of its maritime boundaries and access to key waterways and trade routes.