Consider a planet identical to Earth except having such high sea levels that most continents never surface, and the only available land is a "small" continent very geographically similar to Australia. Lets say humans nearly identical to ourselves evolve on this landmass, along with similar animals that exist today.
How would this world differ from Earth in terms of population, sustainability, war, infrastructure, and technology?
The main difference is that naval technology would never become a big influence. There would be limited trade along the coast but considering any ship leaving the coast could sail for a very long time and find nothing it is unlikely that it would receive much ongoing investment.
The sustainable population would be similar to Australia of the same technology level. Note though that Australia has vast areas of desert that reduce how many people it can support.
The advancement of technology and the sciences may well happen but would likely be slower than in our own world as there are fewer people to come up with the ideas and fewer cultures to share ideas between.
I'd say that there wouldn't be much difference. Australia was a pretty isolated continent before the 18th century so you could make the case that your continent would develop in almost the same way as Australia.
Assuming that this continent has a similar climate, geography and resources to Australia, I'd say the following:
Population: Given what we know about Australian history pre-colonization, human populations and societies would remain relatively primitive. Perhaps if these humans begun forging tools and weapons out of metals, this society could develop like ours has today.
Sustainability: If the society on your continent became very large and unsustainable, then people may first go on expeditions at sea looking for fabled "lost" lands or mythical continents that people could migrate to. When all these expeditions fail and science develops, the next logical step would be for these societies to send expeditions into the "submerged lands" to look for resources.
Perhaps over time, your human society could evolve to live under water. They could leave their ancestral dry lands for a brighter future under the sea?
War: Primarily guerrilla warfare using primitive weapons (spears, shields, arrows, slings, clubs). In an advanced society, i suppose naval warfare would occur if competing factions vied for resources in "submerged lands" of the coast of the continent. Warfare involving cavalry would become very popular on Australia's large flat landmasses.
infrastructure Societies on your continent would be bound to develop advanced infrastructure over time. Stone/mud huts and wooden houses are definitely possible. From then on, who knows. All you would need is some brilliant mind to discover concrete and the world is your oyster.
Technology Basically same as above. All it takes is for one brilliant mind to put two and two together and shout "eureka" when discovering something brilliant.
