Some countries have a significant amount of a particular type of structure or monument. Essentially, one wonders (and surely ICOMOS also does) when a state party reaches the point of "too much of the same" or well-represented features. I've ignored castles and churches, but it might be interesting to highlight these varying and distinct staples of different state parties.

Netherlands (Waterworks)
- Defence Line of Amsterdam
- Droogmakerij de Beemster (Beemster Polder)
- Ir.D.F. Woudagemaal (D.F. Wouda Steam Pumping Station)
- Mill Network at Kinderdijk-Elshout
- Schokland and Surroundings
- Seventeenth-Century Canal Ring Area of Amsterdam inside the Singelgracht
TWHS - Nieuwe Hollandse Waterlinie

United States (Earthwork Mounds)
- Cahokia Mounds State Historic Site
- Monumental Earthworks of Poverty Point
TWHS - Hopewell Ceremonial Earthworks (2017)
TWHS - Serpent Mound

Republic of Korea (Fortifications)
- Hwaseong Fortress
- Namhansanseong
TWHS - Seoul City Wall (2017)
TWHS - Naganeupseong Town Fortress (2020)
TWHS - Ancient Mountain Fortresses in Central Korea

I do think the U.S. focused far too long on natural sites, which admittedly, we are especially rich in. Now it seems as if the focus is on Native American sites - which again are completely worthy, but I'm hopeful we get some diversity and I do see some promise with the Missions, FLW Buildings, Civil Rights, etc.

The Netherlands is DEFINITELY focusing too much on the "man and water" theme. Outside the U.S., I've spent the most time in the UK (a year) and Nederland (6 months) and I explored the Netherlands extensively. There are so many different sites that I think are worth consideration in the Netherlands. I definitely have a bias as I wrote my master's thesis on Dutch colonization in the Americas (sites related to THIS in New York state/New Jersey/ and especiallyNew Castle, DE, [Dutch, Swedish, English, American], would be appreciated too!) and I love all the Low Countries, but I think the Netherlands has so much to offer. Maastricht, Delft, Leiden, Utrecht, (these would all have a great shot, like York, Lincoln, Wells, Winchester, if this were years ago and old towns were still accepted), the Ridderzaal, the Veluwe, Kroller-Muller, post-modern architecture in Rotterdam, Rembrandthuis, Royal Palace/Town Hall in Amsterdam aka The Eighth Wonder of the World, and I also have some ideas for serial nominations as well.

Forgot to add Berlage and the Amsterdam School, as well.

I certainly agree with you about US cultural heritage sites. Yet, I am of the opinion that North America's indigenous heritage is still under-represented. That being said I do want to see more modern architecture like the FLW buildings being inscribed.

Less than 10 Native/Indigenous cultural sites in the North American Continent
SGang Gwaay (Canada)
Head-smashed-in Buffalo Jump (Canada)
Cahokia Mounds State Historic Site (USA)
Monumental Earthworks of Poverty Point (USA)
Mesa Verde National Park (USA)
Chaco Culture (USA)
Taos Pueblo (USA)
Archaeological Zone of Paquimé, Casas Grandes (Mexico)
Rock Paintings of the Sierra de San Francisco (Mexico)

With 12,000 years of history (more than 500 tribes) in a region the size of Europe, I expect more of these diverse cultures to be inscribed on the world heritage list. Some are already being pursued in the Canadian and US tentative list. Nearly all of Canada's nominations are mixed properties.

TWHS - Canada
- Pimachiowin Aki
- Áísínai'pi
- Quttinirpaaq
- Qikiqtaruk

TWHS - USA
- Hopewell
- Serpent Mound

Missing Native/indigenous regions (0) WHS
- Eastern United States
- Great Plains (US)
- Pacific Coast (US)
- Great Lakes (US & Canada)

2 US National Parks would likely be successful as mixed nominations

Great Smoky Mountains National Park
"The park contains evidence of four pre-Columbian Indian cultures: Mississippian, Woodland, Archaic and palaeo-Indian. The early Woodland culture period is of special archaeological importance because it shows the first evidence of organized horticulture in North America, with primitive agriculture on river floodplains. These Indians used the caves for shelters and chipped gypsum and mirabilite off the walls: more than 150 archaeological sites have been identified within the national park." - UNESCO

Grand Canyon National Park
"The park contains more than 2,600 documented prehistoric ruins, including evidence of Archaic cultures (the earliest known inhabitants), Cohonina Indians along the South Rim, and Anasazi Indians on both the South Rim, North Rim, and within the Inner Canyon. Hualapai and Havasupai Indians moved into the canyons at this time, where they remained undisturbed until the Anglo-Americans arrived in 1860. Archaeological remains show the adaptation of human societies to severe climate and physiographic environment." - UNESCO

You're definitely right about Native-American culture still being underrepresented. I think I'm a bit skewed by the drought of sites the U.S. had during the 80s/90s. I am really positive about Hopewell and Serpent Mound. I hate calling it "Montezuma's Castle," but the 12th.-15th century cliff dwellings in Camp Verde, Arizona are different than the much earlier sites that have been inscribed (Burial Mounds, etc.) Is it too close to Taos Pueblo or Chaco Culture? However, it represents Hopi and Yavapi cultures who to my knowledge have no representation. URL Fantastic monument and these are underrepresented Native American cultures from the late-period.

edit: Another interesting addition would be a serial nomination of Navajo monuments. Sorry, I changed it from Anasazi (part of Chaco/Pueblo culture) to Navajo, which is distinct. Places like Monument Valley, Little Colorado River Gorge, Grand Canyon (ofc), The Hubbell Trading Post, Grand Falls, El Capitan, Elephant's Foot, Antelope Canyon, and Canyon de Chelly. Some of these could be inscribed alone - but a Navajo Nation Serial Nomination would be incredible. It would stretch from hundreds of millions years of natural heritage, sacred ground to Navajo, to the Hubble Post (oldest continuously operated trading post in the U.S. [1876]) to the present.

Some of this was discussed in a previous topic.
http://www.worldheritagesite.org/forums/index.php?action=vthread&forum=6&topic=1756

There are so many ruins in the Southwest, and these Native sites while hugely important may be considered Too much of the same when compared to the 3 major WHS sites already inscribed in the region. However, I would certainly support any Navajo (Diné) led nomination. Most of the other National Monuments - Tuzigoot, Montezuma, Wuptaki, Walnut Canyon, Casa Grande, Tonto, Navajo, Canyon de Chelly, Hovenweep, Gila Cliff Dwellings, El Morro, Bandelier, Agua Fria are all fantastic worthwhile places to visit. But can any of them argue OUV? Perhaps, but are they as exceptional as Taos, Mesa Verde, and Chaco?

I would support (3) nominations that would complete the Southwest

1) Grand Canyon National Park (Mixed) + Extension, Little Colorado River Gorge
2) Sinagua Culture (Serial Nomination - Northern Arizona)
3) Ancestors of the Navajo (Diné) Nomination (Canyon de Chelly NM + Navajo NM + Monument Valley) Mixed

I absolutely love your proposals. I think the Grand Canyon as a mixed site with the LCRG is a slam dunk. And having visited some of the Ancestors of the Navajo (Diné) sites, I think they are extremely worthy. Canyon de Chelly, as just one example, fills so many criteria - (ii) Cultural (iii) Cultural, (iv) Cultural, (v) Cultural, perhaps (i) and (vi) [OUV] and also (vii) Natural [undeniable]. Combining that with Navajo NM and Monument Valley, I can't see how that would be rejected.

This would include Wuptaki, Tuzigoot, Montezuma, and Walnut Canyon.

Wikipedia page Sinagua

I've suggested all three to the National Park Service during public comment suggestions for the updated 2016 tentative list. All of the suggested sites were discussed here.

So why, pikkle and winterkjm, do you think that they have never been proposed?

I have just reviewed the 35 sites proposed in the 2008 revision of the US T List (The link to the NPS page cited earlier on this forum is "dead" but the original proposed sites can be determined here - http://www.georgewright.org/tentativelist.html ) - there was nothing there. We discussed the NPS review of the process ( http://www.nps.gov/oia/TLEssayFinal.pdf ) the other day and, as far as I can see the lack of "Native American" sites wasn't highlighted.

I presume Monument Valley would have to be proposed by the Navajo Nation itself and that being a "Tribal Park" would be regarded by the US as being equivalent to being a National monument etc (Is this correct? One of the US "rules" for inclusion in its T List seems to be that the site has to be of this status!). Are the Navajo too concerned with running casinos etc? They have income from mining, wind farms etc etc - are they just not interested (or badly advised?) But, when we visited Monument Valley (many years ago admittedly) the difference between the visitor centre at an NP and that of a Tribal Park was very evident in terms of lack of investment

Could it be that the NPS is too "Nature" oriented to see the potential? Or did they deliberately "step back" in order to allow other organisations to make proposals?

PS - this subject and the last few posts might be better under the "US approach" topic?