"Whirring wings" refers to the United States of America (verse 1). The people being described as bringing gifts is China (verse 2). To understand the prophecy requires the actual meaning of the Hebrew words that translators for some reason ignored.
The nations of the world will be cut down (verses 5-6; Revelation 11:18; Habakkuk 2:13). The nation(s) bringing gifts to honor God in verse 7 will be better off than those that don't.
The prophecy is of a future far from Isaiah's time, which is why it was sealed and not understood (Isaiah 8:16-17). Some prophecies are only understood as they near their time (Daniel 12:9). Verse 3 clearly mentions a time when all the world will be able to see and or hear an event all at the same time. This is only possible with modern communication systems.
If the prophecy referred to events during or near Isaiah's time, then it would be an unfulfilled prophecy. All the world is supposed to be aware of a nation bringing gifts to God, and know what Mount Zion represents (verses 3 & 6). This has never happened yet. Explaining this prophecy as something that has already happened is contradicting the prophecy itself.
Chapter 18 is contrasted with chapter 19. A distant nation not usually associated with God brings gifts, while Egypt a nation next door to Israel is being punished for not knowing better. Isaiah 19:5 predicts the drying of the Nile, confirming this is a prophecy far from Isaiah's time, and most likely in our time (i.e. climate change; melting glaciers).
Hebrew Word Meanings
Since these nations did not yet exist in Isaiah's time, he could only describe them by their long standing character or end state. Thus everything Isaiah mentions should be considered uniquely descriptive, otherwise it would be easily confused with some other nation. An example of this would be the "messengers" in verse 2. Every nation has messengers/ambassadors. How is this nation different? It is different because of the sheer number of ambassadors it sends "over the waters" and not by land.
(The Hebrew words עַל פְּנֵי in verse 2 mean "on upon" the waters or "over upon." It can be taken to mean sailing on the surface of the water, or being above and over the water. Today, ambassadors rarely travel by sea since there are airplanes. This is why they are "swift.")
There is no way of understanding the prophecy without delving into the actual meaning of the Hebrew words Isaiah used to describe these future nations. You can check the meanings on biblehub.com by using their interlinear translations and definitions.
"shadowing" צִלְצַ֣ל The common denominator in the meanings of this word is "noise." It should be left as "noise" because it is uncertain how Isaiah might be using this word to describe what doesn't exist yet.
"wings" כְּנָפָ֑יִם The common denominator in the meanings is "extremity." If "wings" is understood, then the noise of wings would be a natural phenomenon, and not a long standing characteristic of the nation being described. (The noise of wings can also change once birds die out or go away.)
Land of "extreme noise" or "noisy extremes" did not make sense until the modern age of guns, nuclear weapons, jet engines, racing cars and so on. Extreme noise could also describe the character of the people. Americans are the most extroverted and talkative.
"Ethiopia" This word does not exist in Hebrew, only in the New Testament Greek. The word in Hebrew is כֽוּשׁ "Cush." Cush is first mentioned in Genesis 2:13, where it is surrounded by a river (meaning an island or continent). Its boundaries were always vague, and it is unclear what ancient Israel knew of geography after the flood with the division of the earth (Genesis 10:25).
"Along the rivers" or "beyond the rivers"? מֵעֵ֖בֶר Since water surrounds Cush, the land of extreme noise cannot be "along" the rivers, otherwise it would surround Cush entirely and be closer to Israel. If it was a river flowing within Cush, the land of extreme noise would be inside Cush. Thus the only meaning has to be "beyond."
The first verse rephrased: "Woe to the land of noisy extremes beyond the rivers of Cush."
"That sendeth ambassadors-" The word צִירִ֗ים is not ambassadors (the real ambassador/messenger word occurs later). Most of the time this word is translated as "pain" or "pangs" in the rest of the Bible. Its meaning is of physical or mental pressure.
וּבִכְלֵי is translated as "vessels" but the general meaning is "implements" or "instruments."
גֹמֶא֮ is translated as "bulrushes" meaning papyrus or paper.
The Septuagint puts the meaning together as "treaties and paper letters." In modern terms: treaties, agreements, contracts, futures, options, derivatives, currency, guarantees, investment certificates, rights, prohibitions, regulations, sanctions, patents, bonds, stocks, and so on. The modern world runs on paper agreements and paper instruments. The land of extreme noise puts out more of these than any other nation. Every dollar is a contract the US government will in theory honor. When these fail, (think sub-prime) there is anguish or pain. Contracts also obligate certain responses, which in unfavorable conditions also means distress.
"-to a nation scattered and peeled-" Most of the time, מְמֻשָּׁ֣ךְ "scattered" is spelt quite differently elsewhere in the Bible, but in Proverbs 13:12 there is only a one letter difference. "Hope 'deferred' makes the heart sick." The meaning is "drawn out or delayed" not "scattered." A people long repressed, or suppressed fits the Hebrew meaning.
"-peeled-" וּמוֹרָ֔ט means "obstinate or independent." It is uncertain how the King James translators came up with "peeled."
The KJV translated נוֹרָ֖א as "terrible." The word actually means to be afraid, to be in awe, or to cause fear/awe. As a long term characteristic, "respect" would seem more appropriate than a people perpetually fearful or always causing fear.
קוקו is translated as "meted out" but the meaning is "stalwart."
Verse 2 rephrased: "Go, ye swift messengers, to a nation repressed and independent, to a people respected from their beginning hitherto; a nation stalwart and trampling, whose land the rivers have spoiled."
The Chinese people have always been led by their governments, and repressed by authoritarian rule. Confucian ideals lead to the self-regulation of behavior (self repression). But the country is also independent, different from all others (no alphabet, and a tonal language), self-reliant and self-sufficient. Due to China's natural wealth, numerous people, and for centuries the source of all that flowed on the Silk Road, she has been respected for centuries at a time. China is the oldest continuous civilization on earth (stalwart). Her millions trample the earth just with everyday walking. And China is also a land divided by rivers, and spoiled by rivers when they flood. (The Yellow River is also called "China's Sorrow.")
Is there another nation that fits the meaning of the Hebrew words so well?
The prophecy is now clear. From Israel, looking westwards beyond Africa (Cush), the only nation of note is the United States. This is the nation that sends out over the seas endless paper instruments (financial, and political). America sends ambassadors to China, because China has returned to her historical role as the world's factory.
God has promised America will be cut down before her fruit is ripe (verses 5-6). It is cut down early because it is not being kept (Matthew 13:30). The land of noisy extremes no longer appears in the prophecy. Total destruction or is something left?
Revelation 13:16-17 describes the antichrist system as one that can stop any one from buying or selling. America is the only nation with the power of economic sanctions, stopping not just individuals but entire nations from buying or selling. Revelation 11:18 tells us God will destroy those who destroy the earth. Man could not destroy the earth until he invented machines. America is the only nation that has used nuclear weapons in war.
When this "harvest" occurs, God tells the world to watch as a distant people not normally associated with Him bring gifts to Zion (verse 7). This does not mean China escapes the "Woe" that opens the chapter. Nor does it mean China escapes the cutting down in verses 5 and 6. All nations not measuring up to God's standards will be punished (Zechariah 14:17-19). It just means a part of China survives.
Now it is clear why many translators do not follow the actual Hebrew. They suspect or know the prophecy is against them.