XML Unexpected element, content of the parent element must match type

I'm new to XML (and new to stackoverflow) and I'm trying to write an XML file & an accompanying DTD file containing some basic information about geographic subdivisions (states and provinces). The first of my <Subdivision> elements is working fine, but oXygen is giving me the following error at the start of the second <Subdivision> element:

> Unexpected element "Subdivision". The content of the parent element type must match "(Subdivision)".

I'm not sure what's causing the first one to work and the second one to error, I'm probably missing something but I can't figure out what it is.

Here's the XML code in question, somewhat trimmed:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE Subdivisions SYSTEM "Subdivision.dtd">

<Subdivisions>
	<Subdivision subdivisionName = "Nebraska">
		<official_name>State of Nebraska</official_name>
		<country>United States</country>
		<iso_3166_code>US-NE</iso_3166_code>
		<regional_capital>Lincoln</regional_capital>
		<population>1961504</population>
		<land_area_miles>77358</land_area_miles>
	</Subdivision>
	
	<Subdivision subdivisionName = "Southwest Finland"> <!-- the error is on this line-->
		<official_name>Southwest Finland</official_name>
		<country>Finland</country>
		<iso_3166_code>FI-19</iso_3166_code>
		<regional_capital>Turku</regional_capital>
		<population>481403</population>
		<land_area_miles>4212</land_area_miles>
	</Subdivision>
	
	<!-- trimmed the rest -->

</Subdivisions>

And the DTD that goes with it:

<?xml encoding="UTF-8"?>

<!ELEMENT Subdivisions (Subdivision)>

<!ELEMENT Subdivision (official_name, country, iso_3166_code, regional_capital, population, land_area_miles)>

<!ELEMENT official_name (#PCDATA)>
<!ELEMENT country (#PCDATA)>
<!ELEMENT iso_3166_code (#PCDATA)>
<!ELEMENT regional_capital (#PCDATA)>
<!ELEMENT population (#PCDATA)>
<!ELEMENT land_area_miles (#PCDATA)>

<!ATTLIST Subdivision subdivisionName CDATA #REQUIRED> 

This is my first time doing XML and my first time asking a StackOverflow question so I apologize if I did it wrong or provided too little (or too much?) context/code.

Any help is greatly appreciated!

My friend told me a solution that solved my problem, I didn't know that you can use the + symbol in the DTD file to indicate that there are one or more of an element.

Changed the line

<!ELEMENT Subdivisions (Subdivision)>

to this:

<!ELEMENT Subdivisions (Subdivision+)>