Country.php

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Relations\HasManyThrough;

class Country extends Model
{
    use HasFactory;

    public function posts(): HasManyThrough {
        return $this->hasManyThrough(
            Post::class,
            User::class,
            'country_id',
            'user_id',
            'id',
            'id',
        );
    }
}

Post.php

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Relations\BelongsTo;

class Post extends Model
{
    use HasFactory;

    public function user(): BelongsTo {
        return $this->belongsTo(User::class);
    }
}

User.php

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Relations\BelongsTo;
use Illuminate\Database\Eloquent\Relations\HasMany;
use Illuminate\Foundation\Auth\User as Authenticatable;
use Illuminate\Notifications\Notifiable;

class User extends Authenticatable
{
    use HasFactory, Notifiable;

    public function posts(): HasMany {
        return $this->hasMany(Post::class);
    }

    public function country(): BelongsTo {
        return $this->belongsTo(Country::class);
    }
}