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It's often to do with commercial territory rights under the seabed, Howard.
Territorial waters are one thing, but each state with a shoreline has extended commercial rights within international waters when it comes to oil, gas, or any other possible resources on or under the seabed.
Under international law, islands have a particular advantage, and indeed, adding to the examples you supplied, Turkey is also at loggerheads with Greece, Cyprus and Israel, who have formed a military alliance as a result.
Then there is an additional dispute between China and several other countries in the South China Sea, including Vietnam, the Philippines, Indonesia and a few others.
All said and told, plus any that were left out, this leaves us with Laura Sandys' Home Front ideas of local Green Resources, which I prefer to the fossil-fuel-dependency of the present fossilised system of "pollute what you can as much as you can and pay the price later".