How to add spring to existing maven+hibernate+angular application?

As soon as I start the spring app, it stops. gif showcasing the issue: https://i.gyazo.com/058663ea8aec6d0555de69098219b990.mp4

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I believe it happens because I am missing the following three dependencies:

```
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-validation</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>

```

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My question is how do I go about adding these dependencies? 

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I have tried adding the three dependencies to pom.xml, then reloading the project, just to then observe that the build fails because "it is unable to resolve my three dependencies I just added".

See this gif: https://i.gyazo.com/19658a78be3df8663673dfca9d69ffe7.mp4

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FYI, I can get the spring application to work if I reinitialize a new spring project. The issue I specifically is facing is how to add spring dependencies to an existing intellij project.